The longevity of silane promoted adhesion of surface conditioned metallic materials is of concern in dentistry and poses both a functional and esthetic dilemma for the patient and dental professionals. Several methods for surface conditioning exist, but some are employed more frequently in clinical practice.

This overview aims to characterize and discuss the most commonly used surface conditioning methods based on silanization. The primary chemical features in silane treatment will also be presented.

The literature regarding silane utilization was systematically selected and 68 cited references published during 1967-2005 were reviewed. Technical descriptions of different silica-coating (silicatization) methods are presented and some comparative clinical and in vitro experiences are reported. Some other surface condition methods applied in dental laboratories were also selected for presentation.

It is concluded in this overview tribochemical silica-coating followed by a mandatory silane coupling agent application is a clinically proved, relevant adhesion promotion method to enhance the bonding of resin composites to metallic dental materials.

Matinlinna JP, Vallittu PK. Silane Based Concepts on Bonding Resin Composite to Metals. J Contemp Dent Pract 2007 February;(8)2:001-008.

The aim of this study was to determine the compressive fatigue limits (CFLs) of fractured incisor teeth restored using either a conventional adhesive-composite technique or using fiber-reinforced composites (FRCs).

Fifteen extracted sound upper incisor teeth were prepared by cutting away the incisal one-third part of their crowns horizontally. The teeth were restored using three techniques. Group A (control group) was restored by reattaching the original incisal edge to the tooth. Group B was restored using particulate filler composite (PFC). Group C was restored with PFC and FRC by adding a thin layer of FRC to the palatal surface of the teeth. The bonding system used was a conventional etch system with primer and adhesive. All restored teeth were stored in water at room temperature for 24 h before they were loaded under a cyclic load with a maximum controlled regimen using a universal testing machine. The test employed a staircase approach with a maximum of 10³ cycles or until failure occurred. Data were analyzed using analysis of variance (ANOVA) (p=0.05). Failure modes were visually examined.

Group A (reattaching fractured incisal edge) revealed the lowest CFL values, whereas the creation of a new incisal edge with PFC revealed a 152% higher CFL value compared to Group A. Group C (teeth restored with FRC) revealed a 352% higher CFL than the control group. ANOVA revealed the restoration technique significantly affected the compressive fatigue limit (p<0.001). The failure mode in Group A and B was debonding of the restoration from the adhesive interface. While in Group C, the sample teeth fractured below their cemento-enamel junctions.

These results suggested an incisally fractured tooth restored with the combination of PFC and FRC-structure provided the highest CFL.

Garoushi SK, Lassila LVJ, Vallittu PK. Fatigue Strength of Fragmented Incisal Edges Restored with a Fiber Reinforced Restorative Material. J Contemp Dent Pract 2007 February;(8)2:009-016.

The aim of the present study was to investigate the effectiveness of one total-etch self-priming adhesive and two one-step self-etching adhesive systems on the adhesion of a resin composite to both dentin and enamel. The effect of thermocycling on the adhesion was also investigated. The null hypothesis tested was thermocycling would not affect bond strengths to enamel and dentin treated with self-etching adhesives or a total-etch adhesive.

Two single-step self-etching adhesives [Xeno III (XE3) and Prompt L-Pop (PP)] and one two-step total-etch adhesive system (Prime & Bond NT) (P&B NT) were used in this study. Thirty cariesfree unrestored human third molars were used to make specimens of enamel and dentin. Different adhesives were applied on enamel and dentin surfaces according to the manufacturer's instructions then hybrid composite restorative material was condensed on the surface using a mold. The bonded specimens were stored in distilled water at 37°C for 24 hours before being tested. Half of the bonded specimens were tested for shear bond strength without thermocycling. The other half of the test specimens were thermocycled using a thermocycling apparatus in water baths held at 5°C and 55°C with a dwell time of one minute each for 10,000 cycles prior to shear testing. The mean shear bond strength before and after thermocycling was calculated, and the results were subjected to two-way analysis of variance (ANOVA) and repeated measure design to show the interaction between different materials and different times.

The results showed shear bond strength on both enamel and dentin of the total-etch adhesive and the self-etching adhesives decreased after the specimens were subjected to thermocycling.

The null hypothesis tested “thermocycling would not affect bond strengths treated with selfetching adhesives” was rejected. Furthermore, the study revealed the following:

El Araby AM, Talic YF. The Effect of Thermocycling on the Adhesion of Self-etching Adhesives on Dental Enamel and Dentin. J Contemp Dent Pract 2007 February;(8)2:017-024.

The aim of this study was to determine in vitro the shear bond strength (MPa) and the type of bond failure when resin-modified glass ionomer cement (RMGIC) was bonded with different tooth-colored restorative materials.

The RMGIC tested was Fuji II LC (FL) and the tooth-colored restorative materials used were composite resin Point-4 (P4), Compomer Dyract AP (DY), and Ormocere Admira (AD). A total number of 60 FL specimens were prepared using Teflon molds. The specimens were divided into six equal groups. Each group of ten specimens was bonded to a tested tooth-colored restorative material as follows: Group I - etched FL bonded to P4; Group II - non-etched FL bonded to P4; Group III - etched FL bonded to DY; Group IV - non-etched FL bonded to DY; Group V - etched FL bonded to AD; and Group VI - non-etched FL bonded to AD. The specimens were stored in distilled water at 37°C for 24 hours. The shear bond strength was measured in a universal testing machine, and the fractured surfaces were examined under a stereomicroscope.

The results of the shear bond strength indicated the lowest mean value (14.46 MPa) was in Group III, and this was significantly different from the values of other groups (p<0.05). However, Groups V and VI recorded the highest mean values (24.5 MPa and 28.39 MPa) which were significantly different (p<0.05) when compared to other groups. Groups I, II, and IV showed no significant difference with mean values of 20.06, 19.99, and 20.1 MPa which were significantly different from other groups (p<0.05).

AD showed the highest shear bond strength to RMGIC. All groups demonstrated a cohesive failure in FL except for Group IV where a cohesive failure in DY was recorded. AD showed good shear bond strength when laminated with FL.

Taher NM, Ateyah NZ. Shear Bond Strength of Resin Modified Glass Ionomer Cement Bonded to Different Tooth-Colored Restorative Materials. J Contemp Dent Pract 2007 February;(8)2:025-034.

The purpose of this study was to evaluate the effectiveness of three commercially available light emitting diode (LED) light curing units (LCU) (Elipar FreeLight - 3M ESPE; UltraLume LED2 - Ultradent; and Single V - BioArt) for polymerizing Z250-A3 composite (3M ESPE) using Knoop hardness, polymerization depth, and flexural strength properties.

The XL 2500 (3M ESPE) LCU, which is a conventional halogen unit, was used as a control. In all cases the curing time was 20 seconds. Hardness was determined 24 hours after composite cure for 10 samples of 8 mm diameter and 2 mm height for each LCU tested. Samples were stored dry in a lightproof container prior to testing. The depth of cure of the composite was measured immediately after composite polymerization for each LCU using three samples 4 mm in diameter and 6 mm in height. Flexural strength was determined for five samples 24 hours after immersion in distilled water at 37°C. Each sample measured 25 mm in length, 2 mm in width, and 2 mm in height for each LCU tested.

The results were treated statistically for comparison of the LCUs. In all cases the results obtained by LED LCUs were not different or were higher than a conventional halogen LCU.

Second generation LED LCUs were as effective as/or more effective than a halogen LCU for polymerization of the used composite. The present study shows second generation LEDs have the potential to replace halogen LCUs.

Campregher UB, Samuel SMW, Fortes CBB, Medina ADC, Collares FMC, Ogliari FA. Effectiveness of Second-generation Light-emitting Diode (LED) Light Curing Units. J Contemp Dent Pract 2007 February;(8)2:035-042.

Light-emitting diode (LED) polymerization of dental restorative materials has become increasingly popular. However, individual light-curing unit (LCU) functions (intensity and/or wavelength emission) may not conform to manufacturer specifications due to quality control issues. The purpose of this study was to evaluate the quality of irradiance, in terms of power density (intensity) and spectral distribution (peak wavelength), emitted from LED and quartz-tungsten halogen (QTH) LCUs in vitro. The battery expenditure of these LED units was also tested.

The intensity and spectral distribution from four third generation LED (Smartlite PS, Coltolux LED, radii Plus, Diopower) and one QTH (Schein Visible Cure) light sources were measured using six different dental curing light meters (Coltolux, Cure Right, Demetron 100, Demetron LED., Hilux, and Light Meter-200) and a visible-ultraviolet light spectrophotometer (Hitachi Elmer-Perkins). The battery life was also plotted for each light source following a 1500 second duration period. The data obtained from radiometric and spectrophotometric analysis was compared to manufacturer specifications.

Radiometric evaluation revealed LED light units tested did not satisfy manufacturer claims for minimum intensities. Spectral emissions from the LED light sources did meet manufacturer requirements. No clinically appreciable battery drain was evidenced from testing all re-chargeable LED units.

Despite limitations LED technology appears to be an effective alternative for curing of lightactivated esthetic restorative materials. Additional advantages associated with LED curing lights include ergonomic handling capabilities, negative heat generation, and minimal maintenance concerns.

Owens BM, Rodriguez KH. Radiometric and Spectrophotometric Analysis of Third Generation Light- Emitting Diode (LED) Light-Curing Units. J Contemp Dent Pract 2007 February;(8)2:043-051.

The purpose of this study was to compare the surface hardness of a hybrid composite resin polymerized with different curing lights.

Two 3.0 mm thick composite resin discs were polymerized in a prepared natural tooth mold using: (1) a conventional quartz-tungsten halogen light (QTH- Spectrum 800); (2) a high-intensity halogen light, Elipar Trilight (TL) - standard/exponential mode; (3) a high-intensity halogen light, Elipar Highlight (HL) - standard/soft-start mode; (4) a light-emitting diode, Elipar Freelight (LED); and (5) a plasma-arc curing light, Virtuoso (PAC). Exposure times were 40 seconds for the halogen and LED lights, and three and five seconds for the PAC light. Following polymerization, the Knoop hardness was measured at the bottom and the top surfaces of the discs.

Significant differences were found between top and bottom Knoop Hardness number (KHN) values for all lights. The hardness of the top and bottom surfaces of both specimens cured by the PAC light was significantly lower than the other lights. No significant hardness differences were observed between the remaining curing units at the top of the 2.0 mm specimens. Significant differences were found between the LED and two modes of HL on the bottom surfaces. For the 3.0 mm thick samples, while significant differences were noted between LED and TL standard mode and between the two TL curing modes on the top, significant differences were only observed between QTH and the standard modes of TL and HL at the bottom.

Yazici AR, Kugel G, Gül G. The Knoop Hardness of a Composite Resin Polymerized with Different Curing Lights and Different Modes. J Contemp Dent Pract 2007 February;(8)2:052-059.

The aim of this study was to compare the effectiveness of five self-etching and etch-rinse dentin-bonding agents in achieving a gap-free adaptation between the restorative material and the dentin in primary and permanent teeth.

Gaps located at the restoration dentin interface were evaluated using scanning electron microscopy (SEM).

There were more gaps on the corner of the cavities, but no significant difference was detected between different cavity walls (p>0,05). Statistical results of the SEM analysis revealed fewer gaps in the restorations made with self-etching dentin bonding agents than etch-rinse agents at the restoration-dentin interface in both primary and permanent teeth.

Self-etching bonding systems were preferable in primary and permanent teeth according to the results of this study. However, further studies should be conducted to determine a favorable strategy to eliminate the gaps on the corners of cavities and maintain a gap-free adaptation between resin composite and tooth structure.

Tulunoglu O, Ulker AE. Gap Formation between Different Cavity Walls and Resin Composite Systems on Primary and Permanent Teeth. J Contemp Dent Pract 2007 February;(8)2:060-069.

The aim of this study was to evaluate the influence of four photoactivation systems [quartz tungsten halogen (QTH), light-emitting diode (LED), argon ion laser (AL), and plasma arc curing PAC)] on cementum/ dentin and enamel microleakage of Class II restorations using a microhybrid [Z250 – 3M ESPE] and two packable composites [(SureFil - Dentsply and Tetric Ceram HB – Ivoclair/Vivadent].

Three hundred sixty “vertical-slot Class II cavities” were prepared at the mesial surface of bovine incisors using a 245 carbide bur in a highspeed handpiece. Specimens were divided into twelve groups (composite-photoactivation systems). Half of the specimens had the gingival margin placed in enamel (n=15) and the other half in cementum/dentin (n=15). Composites were inserted and cured in 2 mm increments according to manufacturers’ recommended exposure times. After polishing, the samples were immersed in 2% methylene blue solution, sectioned, and evaluated at the gingival margins. Data were submitted to statistical analysis using the Kruskal–Wallis and Mann-Whitney tests.

No significant differences were found among the photoactivation systems and among resin composites (p>0.05). Microleakage was not significantly affected by location (enamel vs. cementum/dentin, p>0.05). These findings suggested neither the photoactivation systems nor the resin composite types might have an effect on the microleakage at gingival margins Class II cavities.

Cavalcante LMA, Peris AR, Ambrosano GMB, Ritter AV, Pimenta LAF. Effect of Photoactivation Systems and Resin Composites on the Microleakage of Esthetic Restorations. J Contemp Dent Pract 2007 February;(8)2:070-079.

The disadvantages of light cured composite resin materials with respect to microleakage are predominantly a result of polymerization shrinkage upon curing. It has been shown curing methods play a significant role in polymerization shrinkage of light-cured composite resins. The purpose of this study was to investigate the effect of light-emitting diode (LED) light curing units (LCUs) compared with a halogen LCU on microleakage of three different flowable composites using self-etch adhesives.

A total of 63 extracted human premolars were prepared with standardized Class V cavity preparations on the buccal and lingual surfaces of each tooth. The occusal margin of the cavities was located on the enamel and the gingival margin was on dentin. Teeth were randomly assigned to three groups of 21 teeth each as follows: Group 1: Adper Prompt L-Pop + Filtek Flow (3M ESPE); Group 2: AdheSE + Tetric Flow (Ivoclar, Vivadent); and Group 3: Clearfil Protect Bond + Clearfil Protect Liner F (Kuraray Medical Inc.). All the groups were subdivided into three groups according to the curing lights used (n=7). Two LED LCUs, Elipar FreeLight and Elipar FreeLight 2 (3M ESPE), and one halogen-based LCU, Hilux Expert (Benlioglu), were used. All teeth were then immersed in 0.5% basic fuchsin dye solution for 24 hours after thermocycling (500 cycles; between 5°C to 55°C). The teeth then were longitudinally sectioned and observed under a stereomicroscope (40X magnification) by two examiners. The degree of dye penetration was recorded separately for enamel and dentin. Data were analyzed with the Kruskal-Wallis and Mann-Whitney tests with the Bonferroni correction.

No statistically significant differences in microleakage were observed between groups either on enamel or dentin (p>0.05).

With the limitation of this in vitro study, the differences in microleakage between LCUs used were not statistically significantly different. Elipar Free Light 2 reduces curing time which can be considered as an advantage.

Attar N, Korkmaz Y. Effect of Two Light-emitting Diode (LED) and One Halogen Curing Light on the Microleakage of Class V Flowable Composite Restorations. J Contemp Dent Pract 2007 February;(8)2:080-088.

The purpose of this in vitro study was to examine the effect of two different finishing systems on the surface roughness of different types of composite restorative materials.

Thirty specimens, 8 mm in diameter and 3 mm in depth, were prepared using a microfill composite (Clearfil ST, Kuraray Co. Ltd., Osaka, Japan), a hybrid composite (Clearfil AP-X, Kuraray Co. Ltd., Osaka, Japan), and a packable composite (Clearfil Photo Posterior, Kuraray Co. Ltd., Osaka, Japan) cured against a Mylar matrix strip to create a baseline surface. The average surface roughness was measured using a surface profilometer (Surftest 211, Mitutoyo, Japan) in five different positions on each sample before and after finishing with one of the two finishing systems [Sof-Lex discs (3M) and Po-Go (Dentsply)]. The obtained data were analyzed by two-way analysis of variance (ANOVA) at a p=0.05 significance level.

There were statistically significant differences in the average surface roughness (Ra, ìm) between the Mylar matrix strip, Sof-Lex discs, and Po-Go discs (p<0.05). For all tested materials, the Mylar matrix strip provided smoother surfaces than both of the finishing systems (p<0.05). When the finishing discs were compared, Sof-Lex discs produced a smoother surface than Po-Go discs for all tested materials (p<0.05).

The Mylar matrix strip provided a smoother surface than Sof-Lex and Po-Go discs. Furthermore, Sof-Lex discs produced smoother surfaces than Po-Go discs. Sof-Lex and Po-Go systems produced clinically acceptable surface roughness for microfill, hybrid, and packable composite resin materials. The effect of finishing and polishing systems on surface roughness was dependent on both the system and the composite resin restorative material.

Üçtaşli MB, Arisu HD, Ömürlü H, Eligüzeloğlu E, Özcan S, Ergun G. The Effect of Different Finishing and Polishing Systems on the Surface Roughness of Different Composite Restorative Materials. J Contemp Dent Pract 2007 February;(8)2:089-096.

The aims of this study were to investigate the influence of commercially pure titanium (PTi) and titaniumaluminum- vanadium (Ti-6Al-4V) alloys (TiA) on the final shade of low-fusing porcelain bonded to them and to compare the shade changes with those of three conventional metal-ceramic systems.

A titanium casting unit was used to cast PTi and Ti-6Al-4V alloy specimens followed by A3 shade low-fusing porcelain (Noritake) being bonded to them. Gold-based (AuA), palladium-based (PdA), and nickel-chromium (Ni-Cr) alloys were cast with an automatic centrifugal casting machine, then A3 shade conventional porcelain material (Vita, VMK 95) was applied to them. Ten specimens of each metal were then fabricated. The CIE L* a* b* color coordinates of the specimens were measured with a spectrophotometer.

All alloys had significant color changes when compared with A3 shade tabs. The color differences from the shade tabs were 5.79 for the Ti-6Al-4V group, 6.46 for PdA alloy, 8.12 for AuA alloy, 8.15 for Ni-Cr alloy, and 12.58 for PTi. The specimens differed from the shade tabs primarily because of the differences in a* and b* coordinate values.

Predictable shade reproduction of metal-ceramic restorations (MCRs) may be impaired by the underlying metal. The PTi had the greatest color differences among all the tested metal when compared with the shade tabs, whereas the Ti-6Al-4V alloy had the lowest. PTi is more likely to affect the final shade of low-fusing porcelain than Ti-6Al-4V alloy.

Al Wazzan KA, Al Hussaini IS. The Influence of Commercially Pure Titanium and Titanium-Aluminum- Vanadium Alloy on the Final Shade of Low-fusing Porcelain. J Contemp Dent Pract 2007 February;(8)2:097-104.

The aim of this study was to evaluate the bond strength and crown-repair material interface of polycarbonate crown repaired using flowable resin composite and hybrid resin composite following two different surface preparations.

The facial surfaces of fifty-two polycarbonate crowns were flattened and roughened. Specimens were then divided into four test groups. A bonding agent alone (Groups 1 and 2) or a combination of methylmethacrylate (MMA) + bonding agent (Groups 3 and 4) was applied to the prepared surfaces. Then either a flowable (Groups 1 and 3) or a microfilled hybrid (Groups 2 and 4) resin composite was placed on the surfaces. Forty-eight of the original fifty-two specimens were used for shear bond strength testing. Failure types (adhesive, cohesive, and mixed) were evaluated. The remaining four specimens, one from each group, were used for crown-resin composite interface analysis using a scanning electron microscope (SEM).

There were significant differences in both mean shear bond strength values and failure types (P<0.05). The SEM evaluation revealed a close interface relationship in Groups 3 and 4.

MMA monomer application on a polycarbonate crown prior to application of an adhesive agent improved the shear bond strength of the repair material.

Yilmaz A. A Comparison of Two Different Methods and Materials Used to Repair Polycarbonate Crowns. J Contemp Dent Pract 2007 February;(8)2:0105-112.

The aim of this study was to evaluate the microleakage at gingival margins below the cementoenamel junction (CEJ) of Class II composite restorations using various placement techniques.

Sound human maxillary premolars were selected. Eighty slot-style cavities on the mesial or distal surfaces were prepared with the cervical margins located apical to the CEJ. The specimens were divided into two groups based on the restorative technique utilized (centripetal or incremental). Each group was then categorized into two subgroups according to the type of matrix used resulting in a total of four experimental groups as follows: IP=Incremental and Palodent matrix, IT = Incremental and Transparent matrix, CP = Centripetal and Palodent matrix, and CT = Centripetal and Transparent matrix.

Following restoration with a total etch adhesive (Single Bond) and a resin composite (Z100), the teeth were thermocycled. Then specimens were immersed in 0.5% basic fuchsin dye for 24 hours at a temperature of 37°C. Sectioned restorations were examined under a stereomicroscope (40X magnification), and the extent of the microleakage was scored and recorded. Data were analyzed using the Kruskal-Wallis non-parametric statistical test (P=0.05).

In the four groups of the study no significant differences in the mean rank of microleakage were observed (p>0.05).

When the gingival margin was located on cementum, the kind of matrix and filling technique did not reduce the microleakage.

Ghavamnasiri M, Moosavi H, Tahvildarnejad N. Effect of Centripetal and Incremental Methods in Class II Composite Resin Restorations on Gingival Microleakage. J Contemp Dent Pract 2007 February;(8)2:113-120.

This article proposes and describes the split-increment technique as an alternative for placement of composite resin in large cervical carious lesions which extend onto the root surface.

Two flat 1.5 mm thick composite resin increments were used to restore these cervical carious lesions. Prior to light-curing, two diagonal cuts were made in each increment in order to split it into four triangular-shaped flat portions. The first increment was applied to cover the entire axial wall and portions of the four surrounding walls. The second increment was applied to fill the cavity completely covering the first one and the rest of the four surrounding walls as well as sealing all cavity margins.

This technique results in the reduction of the C-factor and the generated shrinkage stresses by directing the shrinking composite resin during curing towards the free, unbonded areas created by the two diagonal cuts. The proposed technique would also produce a more naturally looking restoration by inserting flat dentin and enamel increments of composite resin of a uniform thickness which closely resembles the arrangement of natural tooth structure.

Hassan KA, Khier SE. Split-increment Technique: An Alternative Approach for Large Cervical Composite Resin Restorations. J Contemp Dent Pract 2007 February;(8)2:121-128.