Current status of luting agents for fixed prosthodontics

In vitro tensile strength of luting cements on metallic substrate

The aim of this study was to determine the tensile strength of crowns cemented on metallic substrate with four different types of luting agents. Twenty human maxillary molars with similar diameters were selected and prepared to receive metallic core castings (Cu-Al). After cementation and preparation the cores were measured and the area of crown's portion was calculated. The teeth were divided into four groups based on the luting agent used to cement the crowns: zinc phosphate cement; glass ionomer cement; resin cement Rely X; and resin cement Panavia F. The teeth with the crowns cemented were subjected to thermocycling and later to the tensile strength test using universal testing machine with a load cell of 200 kgf and a crosshead speed of 0.5 mm/min. The load required to dislodge the crowns was recorded and converted to MPa/mm(2). Data were subjected to Kruskal-Wallis analysis with a significance level of 1%. Panavia F showed significantly higher retention in core casts (3.067 MPa/mm(2)), when compared with the other cements. Rely X showed a mean retention value of 1.877 MPa/mm(2) and the zinc phosphate cement with 1.155 MPa/mm(2). Glass ionomer cement (0.884 MPa/mm(2)) exhibited the lowest tensile strength value. Crowns cemented with Panavia F on cast metallic posts and cores presented higher tensile strength. The glass ionomer cement showed the lowest tensile strength among all the cements studied.

Retentiveness of metal coping luted to teeth of uremic patients undergoing hemodialysis using five different luting cements

OBJECTIVES

This study aimed to assess the retention of metal copings luted to uremic teeth with five different luting agents.

METHODS

A total of 35 sound natural molars was collected from uremic patients and randomly assigned into five groups (n=7). The teeth were prepared for metal copings using diamond tips and water coolant. Metal copings with a loop on the occlusal surface were fabricated using base metal alloy (Rexillium III). The copings were luted using Fuji I, glass ionomer (GI); Fuji Plus, resin-modified glass ionomer (RMGI); Panavia F 2.0, resin cement; Rely X Unicem, self-adhesive cement (SA); and Adhesor, zinc phosphate cement (ZPh). All specimens were incubated at 37°C for 24 hours, conditioned in artificial saliva for 7 days, and then thermocycled for 5000 cycles (5°C-55°C). The dislodging force was measured using a universal testing machine at a crosshead speed of 2 mm/min. The mode of failure of the loaded adhesive copings was evaluated. Statistical analyses were performed using one-way analysis of variance and Tukey post hoc test.

RESULTS

GI and SA cements had the highest and the lowest mean retentive strength, respectively (580.90±17.3, 406.6±12.7). There was no significant difference between ZPh, SA, and resin cements. These cements were inferior to GI and RMGI cements (p<0.05), which showed statistically similar retentive strengths.

CONCLUSIONS

The results of this study support the use of glass ionomer and resin-modified glass ionomer cements for luting of metal copings to uremic teeth with retentive preparations.

Effect of different airborne-particle abrasion/bonding agent combinations on the bond strength of a resin cement to a base metal alloy

STATEMENT OF PROBLEM

Investigation of surface treatments to improve the bond of resin cements to metals may contribute to the longevity of metal ceramic restorations.

PURPOSE

The purpose of this study was to evaluate the efficacy of surface treatments on the shear bond strength (SBS) of a resin cement to nickel-chromium (NiCr) alloy.

MATERIAL AND METHODS

Eighty cast NiCr alloy disks (9 × 3 mm) were divided into 8 groups (n=10), which received 1 of the following surface treatments: 1) 50 µm Al(2)O(3) particles + silane; 2) 120 µm Al(2)O(3) + silane; 3) 30 µm silica-modified Al(2)O(3) (Cojet Sand) + silane; 4) 120 µm Al(2)O(3) followed by 110 µm silica-modified Al(2)O(3) (Rocatec) + silane; 5) 50 µm Al(2)O(3) + metal primer; 6) 120 µm Al(2)O(3) + metal primer; 7) 30 µm silica-modified Al(2)O(3) (Cojet Sand) + metal primer; and 8) 120 µm Al(2)O(3) followed by 110 µm silica-modified Al(2)O(3) (Rocatec) + metal primer. The silane was RelyX Ceramic Primer and the metal primer Alloy Primer. RelyX ARC resin cement was bonded to NiCr alloy surfaces. Specimens were thermally cycled before shear mode testing. Data (MPa) were analyzed by 1-way ANOVA and the Tukey test (α=.05). Failure mode was determined with a stereomicroscope (×20).

RESULTS

The results revealed that surface treatment was significant (P<.001). There was no significant difference between 50 µm and 120 µm Al(2)O(3) particles, regardless of the bonding agent used (silane or metal primer). Cojet Sand provided lower SBS than Rocatec, both in the groups treated with silane (P<.001) and metal primer (P<.01). No significant difference was observed between silane and metal primer in the groups abraded with 50 µm and 120 µm Al(2)O(3) particles. Metal primer decreased the SBS of both Cojet Sand and Rocatec groups (P<.001). Rocatec + silane had the highest SBS and Cojet Sand + metal primer the lowest. All groups presented 100% adhesive failure.

CONCLUSIONS

Particle size influenced SBS only in the groups abraded with silica-modified Al(2)O(3). The bonding agent did not affect SBS in the groups abraded with Al(2)O(3). Alloy Primer was not chemically compatible with silica-modified Al(2)O(3). Both mechanical (particle size) and chemical (silica/silane interaction) factors contributed to the high SBS of Rocatec + silane.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

Radiopacity evaluation of contemporary luting cements by digitization of images

Objective. The aim of this study was to evaluate the radiopacity of two conventional cements (Zinc Cement and Ketac Cem Easymix), one resin-modified glass ionomer cement (RelyX Luting 2) and six resin cements (Multilink, Bistite II DC, RelyX ARC, Fill Magic Dual Cement, Enforce and Panavia F) by digitization of images. Methods. Five disc-shaped specimens (10 × 1.0 mm) were made for each material, according to ISO 4049. After setting of the cements, radiographs were made using occlusal films and a graduated aluminum stepwedge varying from 1.0 to 16 mm in thickness. The radiographs were digitized, and the radiopacity of the cements was compared with the aluminum stepwedge using the software VIXWIN-2000. Data (mmAl) were submitted to one-way ANOVA and Tukey's test (α = 0.05). Results. The Zinc Cement was the most radiopaque material tested (P < 0.05). The resin cements presented higher radiopacity (P < 0.05) than the conventional (Ketac Cem Easymix) or resin-modified glass ionomer (RelyX Luting 2) cements, except for the Fill Magic Dual Cement and Enforce. The Multilink presented the highest radiopacity (P < 0.05) among the resin cements. Conclusion. The glass ionomer-based cements (Ketac Cem Easymix and RelyX Luting 2) and the resin cements (Fill Magic Dual Cement and Enforce) showed lower radiopacity values than the minimum recommended by the ISO standard.

Diametral tensile strength and film thickness of an experimental dental luting agent derived from castor oil

The need to develop new dental luting agents in order to improve the success of treatments has greatly motivated research.

Pre-heated dual-cured resin cements: analysis of the degree of conversion and ultimate tensile strength

This study evaluated the degree of conversion (DC) and ultimate tensile strength (UTS) of dual-cured resin cements heated to 50º C prior to and during polymerization. Disc- and hourglass-shaped specimens of Rely X ARC (RX) and Variolink II (VII) were obtained using addition silicon molds. The products were manipulated at 25º C or 50º C and were subjected to 3 curing conditions: light-activation through a glass slide or through a pre-cured 2-mm thick resin composite disc, or they were allowed to self-cure (SC). All specimens were dark-stored dry for 15 days. For DC analysis, the resin cements were placed into the mold located on the center of a horizontal diamond on the attenuated total reflectance element in the optical bench of a Fourier Transformed Infrared spectrometer. Infrared spectra (n = 6) were collected between 1680 and 1500 cm-1, and DC was calculated by standard methods using changes in ratios of aliphatic-to-aromatic C=C absorption peaks from uncured and cured states. For UTS test, specimens (n = 10) were tested in tension in a universal testing machine (crosshead speed of 1 mm/min) until failure. DC and UTS data were submitted to 2-way ANOVA, followed by Tukey's test (α= 5%). Both products showed higher DC at 50º C than at 25º C in all curing conditions. No significant difference in UTS was noted between most light-activated groups at 25º C and those at 50º C. VII SC groups showed higher UTS at 50º C than at 25º C (p < 0.05). Increased temperature led to higher DC, but its effects on resin cement UTS depended on the curing condition.

Bonding of restorative materials to dentin with various luting agents

The aim was to compare eight types of luting agents when used to bond six indirect, laboratory restorative materials to dentin. Cylinders of the six restorative materials (Esteticor Avenir [gold alloy], Tritan [titanium], NobelRondo [feldspathic porcelain], Finesse All-Ceramic [leucite-glass ceramic], Lava [zirconia], and Sinfony [resin composite]) were ground and air-abraded. Cylinders of feldspathic porcelain and glass ceramic were additionally etched with hydrofluoric acid and were silane-treated. The cylinders were luted to ground human dentin with eight luting agents (DeTrey Zinc [zinc phosphate cement], Fuji I [conventional glass ionomer cement], Fuji Plus [resin-modified glass ionomer cement], Variolink II [conventional etch-and-rinse resin cement], Panavia F2.0 and Multilink [self-etch resin cements], and RelyX Unicem Aplicap and Maxcem [self-adhesive resin cements]). After water storage at 37°C for one week, the shear bond strength of the specimens (n=8/group) was measured, and the fracture mode was stereomicroscopically examined. Bond strength data were analyzed with two-factorial analysis of variance (ANOVA) followed by Newman-Keuls' Multiple Range Test (α=0.05). Both the restorative material and the luting agent had a significant effect on bond strength, and significant interaction was noted between the two variables. Zinc phosphate cement and glass ionomer cements produced the lowest bond strengths, whereas the highest bond strengths were found with the two self-etch and one of the self-adhesive resin cements. Generally, the fracture mode varied markedly with the restorative material. The luting agents had a bigger influence on bond strength between restorative materials and dentin than was seen with the restorative material.

Conventional and contemporary luting cements: an overview

Long-term clinical success of fixed prosthodontic restorations is influenced by many factors, one important factor being the selection of an appropriate luting agent. No single luting agent is capable of meeting all the stringent requirements, which is one reason why there is such a wide choice of luting agents currently available from conventional water-based to contemporary adhesive resin cements. Introduction of adhesive resin systems has completely changed the face of fixed prosthodontic practice leading to an increased use of bonded all-ceramic crowns and resin-retained fixed partial dentures. This article makes an effort to review various conventional and contemporary luting agents, their properties & associated clinical implications thereby trying to help the clinician select an appropriate luting agent for a given clinical situation.

Nonlinear visco-elastic finite element analysis of different porcelain veneers configuration

This study is aimed at evaluating the biomechanical behavior of feldspathic versus alumina porcelain veneers. A 3D numerical model of a maxillary central incisor, with the periodontal ligament (PDL) and the alveolar bone was generated. Such model was made up of four main volumes: dentin, enamel, cement layer and veneer. Incisors restored with alumina and feldspathic porcelain veneers were compared with a natural sound tooth (control). Enamel, cementum, cancellous and cortical bone were considered as isotropic elastic materials; on the contrary, the tubular structure of dentin was designed as elastic orthotropic. The nonlinear visco-elatic behavior of the PDL was considered. The veneer volumes were coupled with alumina and feldspathic porcelain mechanical properties. The adhesive layers were modeled in the FE environment using spring elements. A 50N load applied at 60 degrees angle with tooth longitudinal axis was applied and validated. Compressive stresses were concentrated on the external surface of the buccal side of the veneer close to the incisal margin; such phenomenon was more evident in the presence of alumina. Tensile stresses were negligible when compared to compressive ones. Alumina and feldspathic ceramic were characterized by a different biomechanical behavior in terms of elastic deformations and stress distributions. The ultimate strength of both materials was not overcome in the performed analysis.

Scanning electron microscopy analysis of dental cements

The aim of this study was to compare in vitro the characteristics of different types of luting cements (zinc phosphate, glass-ionomer and resin based composite cement) using scanning electron microscopy (SEM) analysis and microleakage for the quality range of materials. Dental cements were mixed in accordance with the manufacturer's instructions and formed with posts in dental root canals of extracted teeth. The quality of cement was determined by SEM observation on horizontal sectioned roots with fixed posts according to specific pore and marginal gap diameter. The microleakage was measured on specimens immersed in Lofler (methylene blue) solution. The mean values of the maximal diameter of pores, marginal gaps and microleakage of conventional cements are remarkably larger in comparison with composite luting agents. In conclusion, the quality and efficiency of composite luting agents in comparison with conventional cements are more successful in protecting the interior of tooth from penetration of oral fluids, bacteria and bacterial toxins into unprotected dentine.

Limited Decalcification/Diffusion of Self-adhesive Cements into Dentin

Resin cement diffusion into dentin may differ as a function of the pre-treatment regimen. Since self-adhesive cements do not require substrate pre-treatment for luting, penetration of and interaction with the underlying dentin are questioned. We hypothesized that differences in the resin cement diffusion into dentin may exist among current commercial adhesive cements. Composite cylinders were luted on mid-coronal dentinal surfaces by an etch-and-rinse cement (Calibra), a self-etching system (Panavia F 2.0), and 4 self-adhesive cements (Multilink Sprint, Rely X Unicem, G-Cem, Bis-Cem). Dentin/cement interfacial characteristics were analyzed by a staining technique (Masson’s trichrome) and by scanning electron microscopy. Conventional acid etching resulted in partially infiltrated adhesive interfaces differing from those achieved with the application of self-etching primer. No hybrid layer and/or resin tag formation was detectable at the interfaces bonded with self-adhesive cements. Limited decalcification/infiltration was observed for self-adhesive cements into the underlying dentin. Self-adhesive cements were not able to demineralize/dissolve the smear layer completely.

Effect of cement selection and finishing technique on marginal opening of cast gold inlays

STATEMENT OF PROBLEM

The standard cement for partial-veneer cast gold restorations has been zinc phosphate. With increasing interest in using resin and resin-modified glass ionomer cements for this purpose, marginal adaptation with use of these newer cements must be assessed.

PURPOSE

The purpose of this in vitro study was to determine if the marginal adaptation of cast gold inlays is comparable for 3 different luting agents and 3 finishing techniques.

MATERIAL AND METHODS

Cast gold inlays were cemented into triangular preparations on the buccal surface of 45 extracted human molars. Three operators each used a different technique for finishing margins: finishing during cementation (FD), finishing before cementation (FB), and finishing before and during cementation (FBA). The 15 teeth for each operator were divided into 3 subgroups of 5 each to accommodate 3 cements: zinc phosphate (Fleck's zinc phosphate: ZP), resin-modified glass ionomer (RelyX Luting: RXL), and self-adhesive modified resin (RelyX Unicem: RXU). For all specimens, fine sandpaper disks followed by fine cuttle disks were used for finishing the castings. The marginal gap was measured using a Nikon measuring microscope at x50 magnification. Data were analyzed with a 1-way ANOVA for each cement (alpha=.05).

RESULTS

There were significant differences among finishing techniques for each cement (P<.05). For ZP, the smallest mean marginal gaps were for FD (31 microm) and FBA (42 microm). For RXL, FBA produced the smallest gap (19 microm). For RXU, FB (23 microm) and FBA (22 microm) were optimal.

CONCLUSIONS

Within the limitations of this in vitro study, the marginal gap attained with cementation of partial-veneer cast gold restorations with ZP (31 microm) can also be obtained using RXL or RXU. The techniques of FD or FBA are best used for ZP, whereas the FBA technique is best for RXL, and either FB or FBA is optimal for RXU. The FBA technique yielded a small gap; this was common to all 3 cements.

Influence of endodontic sealers on the bond strength of carbon fiber posts

OBJECTIVE

The aim of this study was to verify the influence of endodontic sealers on the bond strength of an adhesive system and a resin cement used for carbon posts cementation.

METHODS

Thirty extracted human premolars were instrumented and randomly divided into three groups according to the tested sealer: EndoFill, Sealapex, or EndoREZ. Specimens were stored at 37 degrees C. After 48 h, half of specimens were prepared to receive the post and the others after 7 days. The posts were cemented with Adper Single Bond/Rely X ARC and stored in distilled water at 37 degrees C for 7 days. After this period, the specimens were sectioned in three slices (coronal, middle, and apical). The push-out test was performed in a universal machine and the debonded area was examined in a stereomicroscope.

RESULTS

Data were submitted ANOVA and Tukey test (alpha = 0.05). The EndoFill showed lower bond strength than other sealers (p < 0.01). The EndoREZ sealer was statistically greater than other groups for coronal and middle portions and similar for apical portion (p > 0.05). Coronal and middle portions showed the best results for all groups, mainly when the canal preparation was performed after 48 h (p < 0.01). Mixed failure occurs with more frequency (55.6%) followed by failure in adhesive-dentin interface (34.4%) and adhesive-post interface (10.0%).

CONCLUSION

The use of EndoREZ sealer promoted higher bond strength in root coronal and middle portions when carbon post was fixed with a resin cement.

Dental cements for definitive luting: a review and practical clinical considerations

Dental cement used to attach an indirect restoration to a prepared tooth is called a luting agent. A clinically relevant discussion of conventional and contemporary definitive luting agents is presented in this article. Physical properties are listed in table form to assist in comparison and decision-making. Additional subtopics include luting agent requirements, classifications, retention and bonding, cement considerations for implant-supported teeth, and fatigue failure.

Materials. Consensus report of Working Group 4

The method used by the working group was an iterative process based upon a structured review of the relevant literature by a group of rapporteurs. The literature was searched using common databanks (e.g., Medline, Pubmed, Cochrane Library etc.), and also by performing manual searches in the non-indexed literature. The review papers were circulated to the members of the group before and during a conference that served as the basis for subsequent discussions. Each paper was subject to detailed collective analysis and subsequently modified on the basis of panel's discussion and referred to additional relevant literature where appropriate. The consensus statements were prepared after a detailed consideration of the papers submitted to the workshop by the working group. The papers were scrutinized, amended and approved by the group.

To what extent does the longevity of fixed dental prostheses depend on the function of the cement? Working Group 4 materials: cementation

AIMS/BACKGROUND

The objective of this review was to define the impact of cementation mode on the longevity of different types of single tooth restorations and fixed dental prostheses (FDP).

METHODS

Literature search by PubMed as the major database was used utilizing the terms namely, adhesive techniques, all-ceramic crowns, cast-metal, cement, cementation, ceramic inlays, gold inlays, metal-ceramic, non-bonded fixed-partial-dentures, porcelain veneers, resin-bonded fixed-partial-dentures, porcelain-fused-to-metal, and implant-supported-restorations together with manual search of non-indexed literature. Cementation of root canal posts and cores were excluded. Due to lack of randomized prospective clinical studies in some fields of cementation, recommendations had to be based on lower evidence level (Centre of Evidence Based Medicine, Oxford) for special applications of current cements.

RESULTS

One-hundred-and-twenty-five articles were selected for the review. The primary function of the cementation is to establish reliable retention, a durable seal of the space between the tooth and the restoration, and to provide adequate optical properties. The various types of cements used in dentistry could be mainly divided into two groups: Water-based cements and polymerizing cements. Water-based cements exhibited satisfying long-term clinical performance associated with cast metal (inlays, onlays, partial crowns) as well as single unit metal-ceramic FDPs and multiple unit FDPs with macroretentive preparation designs and adequate marginal fit. Early short-term clinical results with high-strength all-ceramic restorations luted with water-based cements are also promising. Current polymerizing cements cover almost all fields of water-based cements and in addition to that they are mainly indicated for non-retentive restorations. They are able to seal the tooth completely creating hybrid layer formation. Furthermore, adhesive capabilities of polymerizing cements allowed for bonded restorations, promoting at the same time the preservation of dental tissues.

Fractured incisors: a judicious restorative approach--Part 2

AIM

To consider different conservative options in the literature to restore fractured anterior teeth.

MATERIALS AND METHODS

Only anterior tooth fractures not involving the pulp were considered, without limitation on age. Treatment options were chosen depending on the clinical situation of patients at first visit. The authors considered 15 cases each of: reattachment; porcelain veneers; direct composites.

RESULTS AND CONCLUSIONS

The techniques analysed were revealed to be valid during the period of observation. No failures were recorded with vital teeth keeping their vitality and no radiographic signs of apical or root pathology. With reattachment, two cases have shown the visibility of fracture line after two years, depending on the angle of light incidence on the tooth surface. For direct restorations, three adult cases have shown partial discolouration at 24, 28 and 40 months. No fractures or debonding have occurred among porcelain veneers. The authors suggest, whenever possible, to utilise the reattachment technique. Direct restorations are suitable for young patients: they have a higher chance of sustaining further trauma than adults, and composites have a favourable failure mode compared to ceramics. In adults, where long-lasting restorations are needed, restoration with porcelain veneers is the treatment of choice.

Cements for use in esthetic dentistry

Dental cements are designed to retain restorations, appliances, and post and cores in a stable and, presumably, long-lasting position in the oral environment. Conventional glass ionomer and zinc phosphate cements are among the most popular materials for luting metallic restorations and posts, whereas resin-based cements are preferred for esthetic applications. Successful cementation of esthetic restorations is largely dependent on the appropriate treatment and silane application to the internal surface of the restoration. Clinicians are frequently advised to use three-step total-etch or two-step self-etch adhesive for luting purposes to avoid problems of incompatibility between adhesives and chemical- or dual-cure cements. A reliable cementation procedure can only be achieved if the operator is aware of the mechanisms involved and the material limitations.

An evaluation of the performance of cast gold bonded restorations in clinical practice, a retrospective study

OBJECTIVES

To evaluate the performance of cast gold bonded restorations in clinical practice.

MATERIALS AND METHODS

The records of all patients treated with cast gold bonded restorations between 1997 and 2004 of The Dental Hospital of Newcastle upon Tyne were reviewed. The following data were recorded: sex of patient, location of teeth (anterior or posterior), position of teeth (upper or lower) and type of cement (glass ionomer, zinc phosphate or resin cement). The survival time was calculated for each restoration; and the reason for failure (either debond or change of treatment plan) identified for each case. The restorations were stratified according to the age of the patient into 10-year age bands and survival analysis was used to identify variables associated with increased risk of failure.

RESULTS

Restorations luted with resin cement showed the highest rate of survival after 7 years of follow-up. The alternative lutes had significantly worse survival (p<0.05). Restorations on anterior teeth had poorer survival than on posterior teeth but there were no differences between those placed in the mandible and the maxilla.

CONCLUSIONS

Within the limitations of this study resin cements are most appropriate for this type of restoration with 80% survival at 7 years. Restorations placed on posterior teeth survived better.

Comparison of the Flexural Strength of Five Adhesive Resin Cements

STATEMENT OF PROBLEM

The increased use of adhesive resin cements in bonded prosthetic restorations has led to restorations debonding under function.

PURPOSE

This investigation evaluated the differences in the flexural strength of new adhesive resin cements as a function of specimen age and storage condition.

MATERIALS AND METHODS

Four new dual-cure cements were compared to C/B Metabond. Twenty specimens of each of the five cements were prepared in a rectangular glass mold (25 x 2 x 2 mm). The new cements were light-activated with a 550 mW/cm(2) lamp for 80 seconds on both the top and bottom surfaces. The auto-cured cement was allowed to set according to manufacturer's directions. Half the specimens were tested immediately after curing while the other half were stored in distilled water at 37 degrees C for 30 days. A three-point bending test was performed using an Instron at a crosshead speed of 1 mm/min. The results were analyzed by analysis of variance and Scheffé tests ( p < 0.05) to examine the effect of specimen age and storage condition.

RESULTS

RelyX ARC exhibited a significantly higher flexural strength compared with Calibra and Panavia F when tested immediately. The standard cement, C/B Metabond, deformed and did not fracture at the immediate test time. After storage, the flexural strength had significantly improved from the immediate test time for Calibra, Cement-It, Panavia F, and C/B Metabond. However, there were no significant differences in the flexural strength among the cements when tested after 30 days in water at 37 degrees C.

CONCLUSION

Immediately after curing, these new adhesive resin cements are not equivalent, as evidenced by the significant variability in the measured flexural strength. The distinctions among the cements diminish after aging in water, which may be due to residual polymerization or a plasticizing effect from water absorption.

CLINICAL SIGNIFICANCE

When light-cured, all the new adhesive resin cements have greater early strengths than the auto-cured cement; however, the wide variation in immediate bending strength suggests that some cements may be more appropriate for use in high-stress clinical situations such as resin-bonded fixed partial dentures.

Dynamometric assessment of the mechanical resistance of porcelain veneers related to tooth preparation: A comparison between two techniques

STATEMENT OF PROBLEM

There is little agreement regarding a palatal extension of the preparation for porcelain veneers, as it represents a more invasive technique than a preparation limited to the facial surface of a tooth.

PURPOSE

The purpose of this study was to detect the stress in maxillary anterior teeth restored with porcelain veneers and compare the resistance to fracture of porcelain veneers prepared using different preparation designs.

MATERIAL AND METHODS

Forty-five maxillary anterior teeth were restored with porcelain veneers and divided into 9 groups as follows: Ca, canines with no preparation; Ca-Ch, canines with palatal chamfer preparation; Ca-W, canines with window preparation; LI, lateral incisors with no preparation; LI-Ch, lateral incisors with palatal chamfer preparation; LI-W, lateral incisors with window preparation; CI, central incisors with no preparation; CI-Ch, central incisors with palatal chamfer preparation; CI-W, central incisors with window preparation. Shear-flexural fracture tests were performed. The fractured specimens were subjected to scanning electron microscope (SEM) analysis. Data were statistically analyzed with univariate analysis of variance and the Tukey post hoc test for multiple comparisons (alpha=.05).

RESULTS

The following mean fracture load values (N) were recorded: Ca, 395 +/- 6; Ca-Ch, 310 +/- 8; Ca-W, 322 +/- 8; LI, 309 +/- 8; LI-Ch, 242 +/- 6; LI-W, 225 +/- 8; CI, 298 +/- 8; CI-Ch, 255 +/- 8; CI-W, 221 +/- 6. The SEM analysis showed that both adhesive and cohesive fractures were primarily concentrated at the cervical region. Statistical analysis showed that both the type of tooth and the design of the preparation significantly influenced the resistance to fracture of the restored teeth (P<.001).

CONCLUSION

The chamfer preparation is recommended for central incisors, whereas the window preparation showed better results for canines. Both preparations can be adopted in the restoration of lateral incisors.

[Impact of various luting cements on the fixed dentures bonding strength]

BACKGROUND/AIM

Various luting cements are used to fix dental crowns to prepared teeth, and should provide an adhesive bond to the tooth structure giving reliable retention. The aim of this study was to establish in vitro which type of the tested luting cement provided the strongest adhesive bond of the prepared teeth to the fixed denture.

METHODS

Testing was carried out on the sample of 100 intact human premolars extracted for orthodontic reasons. The preparation of the teeth was performed by a heavy-duty machine. The surfaces of the prepared teeth were mathematically calculated. Dental crowns from the Nickel-Chromium-Molybenum (Ni-Cr-Mo) alloy were made in a standard fashion, and fixed to prepared teeth (two samples of each group) with 5 different types of luting cements. The strength of force applyed to separate the cast crowns from the prepared teeth was measured by an electronic dynamometer, after 7 days.

RESULTS

The obtained results revealed the connection between the type of luting cement and the values of retention power. The best adhesive bond under the constant convergence angle of the prepared teeth was provided by the resin cement.

CONCLUSION

When choosing a luting cement for fixing dental crowns to prepared teeth, the advantage should be given to the resin cement in case the glassionomers are not available.

Load-fatigue performance of gold crowns luted with resin cements

STATEMENT OF PROBLEM

Resin cements have gained popularity over the past few years because of their improved physical properties. There is a need to test these cements under fatigue loading, as there is growing recognition that fatigue testing is more clinically relevant than traditional monotonic static tests.

PURPOSE

This study investigated the load-fatigue performance of complete gold crowns cemented with 4 types of resin cement.

MATERIAL AND METHODS

Four resin cements (C & B Opaque [CBO], Calibra Esthetic [CE], RelyX Unicem [RU], and Panavia F [PF]) and a control, zinc phosphate cement (HY-Bond [HBZPC]) were tested. Fifty human maxillary premolars were prepared to an occluso-cervical dimension of 4 mm and a convergence angle of 20 degrees. Complete gold crowns were cast (Strator 3) and cemented with 1 of the 5 cements (n=10). A fatigue load of 73.5 N was applied at an angle of 135 degrees to the long axis of each tooth-crown specimen. Preliminary failure was defined as the propagation of a crack in or around the crown luting cement layer. The number of cycles to preliminary failure and the cement failure location were determined. Significant differences in cycles to preliminary failure were assessed by the nonparametric Kruskal-Wallis test, with follow-up Mann-Whitney tests (alpha=.05).

RESULTS

Group CE had the highest rank of cycles to preliminary failure, while HBZPC had the lowest cycles to preliminary failure. Group CE had a significantly higher failure cycle count compared to PF (P=.016), RU (P=.001), and HBZPC (P<.001), but was not significantly different from CBO (P=.112). There was no significant difference in the failure cycle count between RU and HBZPC (P=.070).

CONCLUSION

Not all tested resin cements had a superior fatigue life when compared with zinc phosphate cement. Of the 4 resin cement groups, Groups CE, CBO, and PF were significantly superior to HBZPC.

Shear Bond Strengths of Different Substrates Bonded to Lithium Disilicate Ceramics

The aim of this study was to evaluate the shear bond strengths of pre- and untreated resin core materials to lithium disilicate ceramics. Bond strengths to dental hard tissues served as controls. Ceramic cubes (IPS-Empress II) were luted either with a one-step (Variolink II/Excite DSC) or multiple-step total etching bonding system (Tetric Flow/Syntac Classic) to ground surfaces of human enamel, dentin, and resin core materials (Clearfil Core, Multicore). Resin core materials were additionally pretreated with hydrofluoric acid (HF) or were silica-coated (CoJet System). Shear bond strengths were determined after 24-hour water storage (n=10) and thermocycling (TC) (n=10; 2000 cycles, 5-55 degrees C, 30 seconds). Bond strengths to enamel, dentin, and silica-coated composites were significantly higher compared to untreated and HF-pretreated composites (p<0.05; Tukey B). Indeed, silica coating of the composite resins significantly increased the bond strength to ceramics (p<0.05; Tukey B). Due to the lower bond strength values of ceramics to untreated composite resins (as compared to enamel and dentin), any indication for a resin core build-up prior to the preparation of a ceramic restoration should be considered carefully.

Strength and fracture pattern of monolithic CAD/CAM-generated posterior crowns

OBJECTIVES

This study evaluated the strength and fracture pattern of monolithic posterior CAD/CAM crowns hypothesizing that zinc-phosphate cemented lithium disilicate crowns might show the same fracture strength as adhesively cemented crowns.

METHODS

Two sets of monolithic posterior crowns each with uniform occlusal and lateral wall thickness of 1.5mm were fabricated from three types of block ceramic (1) lithium disilicate glass, (2) leucite glass and (3) feldspathic ceramic using CEREC 3 CAD/CAM. Crowns (n = 15) of ceramics (1), (2) and (3) each were (A) zinc-phosphate cemented, (B) adhesively cemented on resin-based composite dies and loaded until fracture. Load data was analyzed using ANOVA and Scheffé tests. Crack pattern was evaluated on an additional three sample cross-sections for each group at start of fracture.

RESULTS

Radial cracks originated early at the cementation interfaces and cone cracks were observed finally at the loading sites. Mean load values (SD) of A-crowns at fracture start/end (1) 807 (91) N/2082 (192) N; (2) 915 (193) N/1130 (166) N; (3) 985 (199) N/1270 (301) N were all significantly (P < 0.001) lower when compared to their B-crown analogs (1) 1456 (205) N/2389 (84) N; (2) 1684 (395) N/2469 (171) N; (3) 1548 (304) N/2392 (75) N, rejecting the authors hypothesis. A-1 crowns had significantly (P < 0.001) higher fracture load than A-2 and A-3 crowns. The A-1 crown fracture load data, even if significantly (P < 0.001) lower, came close to the B-1 values.

SIGNIFICANCE

Adhesive cementation balanced the strength of weak ceramics with that of strong ceramic and recommended itself for leucite glass ceramic and feldspathic ceramic crowns. Zinc-phosphate cementation appeared feasible for lithium disilicate crowns.

Microleakage of various cementing agents for full cast crowns

OBJECTIVES

To evaluate microleakage and marginal gaps in full cast crown restorations bonded with six different types of cementing agents.

METHODS

Sixty non-carious human premolars and molars were prepared in a standardized manner for full cast crown restorations. The mesial and distal margins were located in dentin, while the vestibular and palatal/lingual margins were located in enamel. Crowns were made from a high-gold alloy using a standardized technique. The specimens were randomized to six groups of cementing agents: one zinc-phosphate cement (Harvard cement), one conventional glass-ionomer cement (Fuji I), one resin-modified glass-ionomer cement (Fuji Plus), two standard resin cements (RelyX ARC, Panavia F), and one self-adhesive universal resin cement (RelyX Unicem). After 4 weeks of storage in distilled water at 37 degrees C, the specimens were subjected to 5000 thermocycles ranging from 5 to 55 degrees C. Then, they were placed in a silver nitrate solution, embedded in resin blocks, and vertically cut in buccolingual and mesiodistal direction. Subsequently, the objects were evaluated for microleakage and marginal gap using a high-resolution digital microscope camera.

RESULTS

A number of inter-group differences were statistically significant. RelyX Unicem showed the smallest degree of microleakage both in enamel and in dentin. Panavia F und RelyX Unicem were associated with significantly larger marginal gaps than all other cementing agents. No association was observed between microleakage and marginal gap other than a weak direct correlation when using Harvard cement on enamel.

SIGNIFICANCE

The cementing agents investigated revealed different sealing abilities. These differences were not associated with specific types of materials.

Microleakage of glass-ionomer cement placed in association with non-setting calcium hydroxide

The purpose of this investigation was to determine whether non-setting calcium hydroxide [Ca (OH)2] cement placed in the root canal system of premolar teeth would affect the subsequent microleakage of a glass-ionomer restoration (GIC). Following selection, 62 human premolar teeth extracted for orthodontic reasons were accessed and root canals prepared according to a standardized procedure. The specimens were then allocated randomly into two major groups each of 30 teeth. Two other teeth were used as a positive and a negative control. The control group was restored with glass-ionomer cement following drying of the canal and placement of a cotton wool pledget. The test group had all canals dressed with non-setting Ca(OH)2 and then was subdivided, one set (n = 22) being restored following conditioning of the access cavity margins, the other (n = 8) having the margins cleaned with a hand excavator. Samples were assessed for microleakage using a two-point scoring system (leakage or no leakage) in conjunction with a clearing technique using AgNO3. Using Fisher's exact test, a statistically significant difference was found between the control and test groups (P < 0.05) but there was no significant difference between the excavated and conditioned cavities (P=0.55). It is concluded that contamination of access cavity margins with Ca(OH)2 during medication of a root canal interferes with the bond of GIC, resulting in increased microleakage in vitro.

Shear bond strength of composite resin cements to lithium disilicate ceramics

The aim of this study was to evaluate the shear bond strength of different commercial composite resin cement systems to lithium disilicate all-ceramic substrate. Five adhesive resin cement systems Panavia 21 and Panavia F (Kuraray), Variolink 2 (Ivoclar-Vivadent), RelyX Unicem Applicap and RelyX ARC (3M ESPE) were used on all-ceramic (IPS Empress 2; Ivoclar-Vivadent) substrate. Shear bond strength of adhesive resin cement to substrate was tested after thermocycling, or without thermocycling (n = 10). Substrate surfaces of the specimen after loading were SEM microscopically examined. The highest bond strengths in water stored conditions were obtained with RelyX ARC (28.7 +/-3.9 MPa), while in thermocycled conditions the highest bonding values were obtained with Variolink 2 (23.2 +/- 7.5 MPa). The lowest values in both water stored (5.8 +/- 4.0 MPa) and thermocycled (2.4 +/- 2.9 MPa) conditions were obtained with Panavia 21. Shear bond strengths appeared to be affected significantly by thermocycling (anova, P < 0.05). It was concluded that there were significant differences between the bond strengths of adhesive resin cements to lithium disilicate substrate.

Influence of cyclic loading and luting agents on the fracture load of two all-ceramic crown systems

STATEMENT OF PROBLEM

Inherent mechanical properties, fabrication techniques, luting agents, and intraoral conditions are primary factors attributing to longevity of all-ceramic crowns. Before doing time-consuming and costly clinical studies, preclinical in vitro studies should be conducted to evaluate the durability of these crowns. Purpose This study investigated the influence of different luting agents and cyclic loading under wet conditions on the fracture load of CAD-CAM and pressable all-ceramic crowns.

MATERIAL AND METHODS

Ninety-six human premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2-mm occlusal reduction, and occluso-gingival height of 5 mm. Sixteen unprepared premolars served as controls. Forty-eight crowns were laboratory fabricated from a lithium disilicate glass-ceramic (IPS-Empress 2), while 48 CAD-CAM crowns were directly fabricated using a leucite-reinforced glass-ceramic (ProCAD) and the Cerec 3 CAD-CAM system. Three luting agents (Panavia F, Superbond C&B and ProTec CEM) were used for cementation (n = 16). After 1 week storage in water, half of the specimens of each subgroup (n = 8) were cyclically loaded and thermal cycled under wet conditions for 600,000 masticatory cycles and 3500 thermal cycles (58 degrees C/4 degrees C; dwell time 60 seconds) in a masticatory simulator. All specimens were loaded in a universal testing machine with the compressive load (N) applied along the long axis of the specimen at a crosshead speed of 1 mm/min until fracture. Fracture load was recorded for each specimen. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences (P =.05).

RESULTS

Cyclic loading significantly decreased the median fracture load of ProCAD crowns luted using Superbond from 987.2 to 786.0 N (P =.014) and those luted using ProTec CEM from 914.4 to 630.7 N (P =.007). Also, the median fracture load of Empress 2 crowns luted using ProTec CEM decreased significantly from 977.3 to 622.9 N (P =.013). However, cyclic loading did not decrease the median fracture load of crowns luted using Panavia F, Empress 2 (P =.431) and ProCAD (P =.128). With the same loading conditions and luting agents, there were no significant differences in the fracture loads of ProCAD and Empress 2 crowns (P >.05).

CONCLUSIONS

Cyclic loading reduced the fracture load of ProCAD crowns luted with Superbond C&B and ProTec CEM and of Empress 2 crowns luted with ProTec CEM.

In vitro shear bond strength of cementing agents to fixed prosthodontic restorative materials

STATEMENT OF PROBLEM

Durable bonding to fixed prosthodontic restorations is desirable; however, little information is available on the strength of the bond between different cements and fixed prosthodontic restorative materials.

PURPOSE

This study determined the shear-bond strength of cementing agents to high-gold-content alloy castings and different dental ceramics: high-strength aluminum oxide (Procera AllCeram), leucite-reinforced (IPS Empress), and lithium disilicate glass-ceramic (IPS Empress 2).

MATERIAL AND METHODS

Prepolymerized resin composite cylinders (5.5 mm internal diameter, n=20) were bonded to the pretreated surfaces of prosthodontic materials. High-gold-content alloy and high-strength aluminum oxide surfaces were airborne-particle-abraded, and pressable ceramics were hydrofluoric acid-etched and silanized prior to cementing. The cementing agents tested were a zinc-phosphate cement (Fleck's zinc cement), glass ionomer cements (Fuji I, Ketac-Cem), resin-modified glass ionomer cements (Fuji Plus, Fuji Cem, RelyX Luting), resin cements (RelyX ARC, Panavia F, Variolink II, Compolute), and a self-adhesive universal resin cement (RelyX Unicem). Half the specimens (n=10) were tested after 30 minutes; the other half (n=10) were stored in distilled water at 37 degrees C for 14 days and then thermal cycled 1000 times between 5 degrees C and 55 degrees C prior to testing. Shear-bond strength tests were performed using a universal testing machine at a constant crosshead speed of 0.5 mm/min. Statistical analysis was performed by multifactorial analysis of variance taking interactions between effects into account. For multiple paired comparisons, the Tukey method was used (alpha=.05).

RESULTS

In a 3-way ANOVA model, the main factors substrate, cement, time, and all corresponding interactions were statistically significant (all P <.0001). In subsequent separate 1-way or 2-way ANOVA models for each substrate type, significant differences between cement types and polymerizing modes were found (all P <.001). None of the cement types provided the highest bonding values with all substrate types.

CONCLUSION

After 14 days of water storage followed by thermal cycling, only the self-adhesive universal resin cement (RelyX Unicem) and 2 of the resin cements (Panavia F and Compolute) exhibited strong bond strengths to specific prosthodontic materials. In contrast, zinc-phosphate, glass ionomer, and resin-modified glass ionomer cements showed the lowest values of all tested cementing agents after 14 days of water storage followed by thermal cycling.

Influence of cement type on the marginal adaptation of all-ceramic MOD inlays

OBJECTIVE

The aim of this study was to investigate the in-vitro marginal adaptation of all-ceramic class II inlays which were luted with conventional multi-stage pre-treatment cements and one new type of cement, which requires no conditioning.

METHODS

The marginal adaptation of 56 all-ceramic inlays was determined with scanning electron microscopy and microleakage tests. The marginal integrity of each tooth was evaluated at cement-dentin and cement-enamel junctions, with regard to the transitions between tooth-cement and cement-inlay. The inlays were luted on human molars with two resin cements, one compomer, one resin modified glass-ionomer and one new resin cement in accordance with the manufacture's recommended pre-treatment. Light- and chemical-curing modifications were investigated. All tests were performed after thermal cycling and mechanical loading (TCML).

RESULTS

For the resin cements and the new material the marginal integrity was higher than 90% before and after TCML. The marginal adaptation was between 55-80% for the resin modified glass-ionomer and lower than 20% for the compomer. The microleakage was lower than 20% for all cements, only the compomer showed values up to 100% penetration.

SIGNIFICANCE

The difference in marginal integrity between the new universal resin cement without any tooth pre-treatment and conventional resin cements after total-etching, priming and bonding was not significant. Resin GIC may be used with restrictions and compomer cement should not be used with all-ceramic class II inlay restorations.

The in vitro effect of pulpal pressure and luting agent on tensile bond strength of complete cast crowns

STATEMENT OF PROBLEM

The degree to which pulpal pressure may affect bond strength of complete cast crowns is unknown.

PURPOSE

The aim of this in vitro study was to evaluate the effect of simulated pulpal pressure on the tensile bond strength of complete cast crowns luted with 2 different cements.

MATERIAL AND METHODS

Forty-eight human mandibular canine teeth were cleaned and stored in saline solution. The crowns were prepared by 1 investigator, and standardization of the preparation was accomplished by fixing a dental handpiece in a parallelometer. Uniform grooves, 0.5 mm in depth, were prepared with burs with depth guides. The complete crowns were prepared with a 0.5-mm shoulder margin. Teeth were randomly divided into 2 groups of 24 teeth each (Group I and Group II). In Group I, bonding and tensile test procedures of the teeth were carried out under simulated pulpal pressure (15 cm of saline solution). In Group II, simulated pulpal pressure was not used. The roots were removed 1 mm below the cementoenamel junction to create direct communication with the pulp chamber. The remaining pulpal tissues were carefully removed, and crowns were embedded in acrylic resin. The acrylic resin was then penetrated by a stainless steel tube that connected the pulp chamber and the barrel of a disposable plastic 5-ml syringe. The pulp chambers were filled with physiological saline solution under elevated pressure to locate the area of greatest permeability on the dentinal surface. Crowns were cast (Co-Cr alloy) with a 20-mm bar to allow testing of the bond strength. Each of the 2 groups were further divided into 2 luting cement groups of 12 each (Group I, A and B, and Group II, A and B). Group IA/IIA and Group IB/IIB specimens were luted with a polycarboxylate luting cement (Poly-F Plus) and an adhesive luting cement (Superbond C&B), respectively. After storage in distilled water for 24 hours, all specimens were subjected to a tensile bond test in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The maximum load at fracture (Newton) was recorded. The results were then evaluated with 2-way analysis of variance and Tukey's honestly significant difference tests (alpha=.05).

RESULTS

Simulated pulpal pressure increased the bond strength of cast complete crowns cemented with an adhesive luting agent (P=.01). No significant difference was found in the bond strength of complete cast crowns cemented with polycarboxylate cement with or without pulpal pressure. Superbond C&B adhesive luting agent showed significantly higher bond strength values for Group I (388.9+/-32.7) and Group II (300.9+/-66.8), when compared with polycarboxylate cement for Group I (221.3+/-17.3) and Group II (186.8+/-38.5) (P=.001).

CONCLUSION

Simulated pulpal pressure had a positive effect on the retention of complete cast crowns when cemented with Superbond C&B adhesive luting agent. Superbond C&B significantly increased the retention of crowns in either the presence or absence of pulpal pressure.