Abstracts of the February 2007  Issue

Gingival seal of deep Class II direct and indirect composite restorations

Brian J. Kenyon, dmd, Daniel Frederickson, dds, ms & Mark S. Hagge, dmd

Abstract: Purpose: To evaluate in vitro the gingival microleakage of Class II direct and indirect composite restorations with cervical margins 0.5 mm apical to the cemento-enamel junction (CEJ). Methods: Mesial-occusal (MO) preparations of similar size were made in 10 homologous pairs of caries-free extracted human third molars. One specimen for each pair was prepared for a direct composite restoration and the other for an indirect composite restoration. Direct preparations were restored per manufacturer’s instructions. Indirect preparations were impressed, and composite restorations were fabricated and cemented with a dual-cure cement. A total-etch technique was used for all restorations. Restorations were finished, polished, stored for 1 week in distilled water at 37°C, thermocycled (5°-55°C x 1000), sealed with fingernail polish (leaving a 1.5 mm open periphery adjacent to the gingival margin), and placed in 0.5% basic fuchsin dye for 24 hours. Teeth were sectioned longitudinally (mesio-distally) within the restoration in two cuts and the four resulting surfaces (two inner cut surfaces, two outer cut surfaces) were evaluated for dye penetration with a x10 stereoscope using a scale of 0 (no penetration) to 4 (dye penetration involving more than half the axial wall). Results: All 20 specimens had at least one score of three (dye penetration involving less than half of the axial wall) or four. Statistical analysis (Wilcoxon paired-sample test) disclosed a significant decrease in the indirect composite microleakage scores for the two outer cuts (P= 0.006, P= 0.002). No significant differences in microleakage scores were found between materials for the inner cut surfaces of the specimens. Overall, the results of die penetration showed no sta-tistical difference between Class II direct and indirect composite restorations for microleakage. (Am J Dent 2007;20: 3-6).

Clinical significance: Gingival microleakage remains a significant problem for Class II direct and indirect composite restorations when the cervical margin is located apical to the CEJ.

: Dr. Brian J. Kenyon, University of the Pacific Arthur A. Dugoni School of Dentistry, 2155 Webster St., Suite 522L, San Francisco, CA, 94115 USA. E-: bkenyon@pacific.edu

All-ceramic partial coverage restorations on natural molars. Masticatory fatigue loading and fracture resistance

Christian F.J. Stappert, dds, ms, dr med dent, Petra C. Guess, dds, dr med dent, Somsak Chitmongkolsuk, dds, dr med dent,  Thomas Gerds, dds, dipl-math, dr rer nat & Jorg R. Strub, dds, dr med dent, phd

Abstract: Purpose: To determine the reliability and fracture resistance of adhesively luted all-ceramic partial coverage restorations (PCR) on natural upper molars after masticatory fatigue loading. Methods: 64 maxillary molars were divided into four groups of 16 specimens each. Control Group NP remained unprepared. Teeth in Groups EM, EX and PC were prepared equally according to standardized guidelines and restored with the following PCR: Group EM= IPS Empress; Group EX= IPS e.max Press; Group PC=ProCAD/Cerec 3. The 48 PCR were all bonded adhesively with dual polymerizing composite (Variolink II). All specimens were subjected to cyclic mechanical loading (1.2 million cycles, 1.6 Hz, invariable occlusal load 49 N) with thermal cycling (5°C/55°C, dwell time 60 seconds, 5500 cycles) in a mastication simulator. Failure was defined by bulk fracture of a specimen. Subcritical crack patterns were observed. Surviving specimens were loaded until fracture in a universal testing machine. The load to fracture values (N) (1.5 mm/minute crosshead speed) were automatically recorded by controlling software. Statistical analysis of the data was performed by Kruskal Wallis test (ANOVA) (α= 0.05) and pair-wise Wilcoxon rank sum test (α= 0.05). Results: All specimens survived mastication simulation. The following median fracture resistance values (N) (IQR= x_.25-x_.75) were recorded: Group-NP 1960 (1481-2228), Group-EM 1400 (1043-1722), Group-EX 1489 (1114-1751), Group-PC 2134 (2052-2391). The load-to-fracture values of Groups NP and PC in particular were significantly higher (P< 0.05) than those of Groups EM and EX. ProCAD restorations demonstrated the best predictability of failure (SD<). Within the limitations of this study, maxillary molars restored with ProCAD PCR showed a similar fracture resistance when compared to natural teeth. Since the majority of IPS e.max Press and ProCad restorations survived loads within the range of physiological mastication forces, both materials appeared to be suitable for the predictable use of posterior partial crowns. (Am J Dent 2007;20:21-26).

Clinical significance: Examined ceramic PCR and preparation design for upper molars demonstrated a high fracture resistance in vitro. All-ceramic PCR can be recommended for clinical applications as a less invasive and high esthetic alternative to complete crown restorations. Further clinical investigations are recommended to verify these potential in vitro results for IPS e.max Press and ProCAD/Cerec 3 materials.

: Dr. Christian Stappert Department of Biomaterials & Biomimetics, New York University College of Dentistry, 345 East 24th Street, Rm 846S, New York, NY, 10010 USA. E-:christian.stappert@nyu.edu

Influence of background color on the color changes of resin composites after accelerated aging

Yong-Keun Lee, dds, ms, phd & John M. Powers, phd

Abstract: Purpose: To evaluate the changes in color and color coordinates after accelerated aging of resin composites depending on the background color. Methods: Color of seven resin composites (14 shades, 1 mm-thick) was measured in the reflectance mode over a zero calibration box, a white background, and a black background. After baseline color measurement, specimens were aged for total energy of 150 kJ/m². Color change after aging was calculated over three backgrounds. Based on the data of A2 shade composites, the influence of the background color on the changes in color (∆E*ab) and changes in three color coordinates (∆L*, ∆a* and ∆b*) after aging was analyzed by ANOVA (P< 0.01). Correlation among the color changes over three backgrounds was determined with a linear regression analysis. Results: Background color influenced ∆E*ab, ∆L*, ∆a* and ∆b* values. There were significant correlations among the color changes over three backgrounds in the reflectance mode (r = 0.95-0.98). (Am J Dent 2007;20: 27-30).

Clinical significance: Color changes over white background were higher than those over zero calibration box or black background, but the discrepancy among the color changes over three backgrounds did not cross the acceptable or unacceptable borderline value (∆E*ab=1.7) of each resin composite tested. Therefore, background color would not be expected to induce clinically significant deviations of color changes after aging.

*: Dr. Y-K. Lee, Department of Dental Biomaterials Science, Dental Research Institute, College of Dentistry, Seoul National University, Seoul, Korea. E-*: ykleedm@snu.ac.kr

Concentration-dependent effect of bleaching agents on microhardness and roughness of enamel and dentin

Juliana Jendiroba Faraoni-Romano, dds, ms, Cecilia Pedroso Turssi, dds, ms, phd & Mônica Campos Serra, dds, ms, phd
 

Abstract: Purpose: To evaluate the microhardness and surface roughness of enamel and root dentin bleached with 10%, 15% and 22% carbamide peroxide agents. Methods: 52 slabs of enamel and root dentin (6 x 3 x 2 mm) were cut from bovine incisors, ground flat and polished. According to a randomized complete block design, enamel and root dentin slabs (n = 13) were independently allocated to be bleached with one of the following carbamide peroxide-containing agents (CP): 10% (Rembrandt Bleaching Gel Plus), 15% (Rembrandt Xtra Comfort), or 22% (Rembrandt Xtra Comfort Ultra Strength). The control groups were mock-treated with artificial saliva. The bleaching procedures consisted of daily application of the agents on dental substrate surfaces for 2 hours, followed by immersion in artificial saliva for 22 hours over 21 days. Knoop microhardness and surface roughness were measured initially, on sound dental tissues, and at the postbleaching phase. Results: In enamel, microhardness attained after bleaching with 10% CP and 15% CP were similar and significantly lower than that observed for the control group. Specimens bleached with CP 22% did not differ from any of the other groups tested. In root dentin, microhardness changes were indistinguishable. ANOVA showed no significant difference among treatments with respect to surface roughness. (Am J Dent 2007;20: 31-34).

Clinical significance: Enamel was altered in terms of microhardness, but not with regard to surface roughness, following the application of home-use bleaching agents. This microhardness change did not seem to be dependent on the concentration of the product used. In root dentin, microhardness and surface roughness changes due to the application of different concentrations of the at-home carbamide peroxide-containing agents tested were indistinguishable.

*: Dr. Mônica Campos Serra, Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, USP, Av. do Café, s/n, Monte Alegre, CEP 14040-904 Ribeirão Preto, SP, Brazil. E-*: mcserra@forp.usp.br

Effects of dental bleaching on micro- and nano-morphological alterations of the enamel surface

Baiping Fu, dmd, Wiebke Hoth-Hannig & Matthias Hannig, phd

Abstract: Purpose: To investigate the effects of dental bleaching on the enamel surface micromorphology using SEM and TEM. Methods: Fine-polished enamel slabs were randomly divided into eight groups (n= 3). Unbleached specimens served as control (1). The enamel slabs were bleached either with home Illuminé 15% for 8 hours per day, over 7 days (2), 14 days (3), 28 days (4), and 42 days (5) or with Whitestrips for 30 minutes each time, for 14 times (6), 28 times (7) and 42 times (8). The micromorphological surface pattern of the specimens was analyzed by SEM. In addition, two specimens per group (1, 2 and 6) were embedded and analyzed by TEM. Results: SEM and TEM findings revealed that dental bleaching with carbamide peroxide or H₂O₂ over short periods of time (Groups 2, 6) caused nano-morphological alterations of the enamel surface, whereas prolonged exposure to the bleaching agents resulted in micro-morphological changes of the enamel surface. Due to the bleaching process, the thickness of the enamel smear layer was significantly reduced. (Am J Dent 2007;20: 35-40).

Clinical significance: Dental bleaching using 15% carbamide peroxide or 6.5% H₂O₂ caused nano- and micro-morphological changes of the enamel surface. Although these minor alterations may not result in major clinical problems, the present results indicated that the bleaching process affected the micromorphological integrity of the enamel surface.

: Dr. Baiping Fu, Department of Stomatology, No. 1 Hospital aff. to Medical College, Zhejiang University, Qingchun Road 79, Hangzhou 310003, China. E-: baiping_fu@yahoo.com

One-year comparison of metallic and translucent matrices in Class II composite resin restorations

Maximiliano Sérgio Cenci, dds, ms, Flávio Fernando Demarco, dds, phd, Cecília Luiz Pereira, dds, Rafael Guerra Lund, dds & Ricardo Marins de Carvalho, dds, ms, phd

Abstract: Purpose: To evaluate the clinical performance of composite restorations performed with two matrix and wedge systems. Methods: Each of 23 subjects received at least one pair of Class II restorations, one with metallic matrix and wooden wedge and the other with polyester matrix and reflexive wedge. One dentist placed 109 Class II restorations, 51 in premolars and 58 in molars, all in occlusion. Most of the cavities were surrounded by enamel. The restorations were evaluated at baseline, and after 12 months using the modified USPHS criteria. All cavities were restored using Single Bond and P-60, according to the manufacturer’s indications. In the metal matrix group, polymerization was performed from occlusal, and in the polyester group, through the reflexive wedge. Statistical analysis was carried out with Chi-square and McNeumar tests. Results: After 12 months, there was a significant increase in marginal staining, and marginal adaptation was affected by clinical service. There were no differences between matrix and wedge systems, neither considering dental groups nor cavity types. (Am J Dent 2007;20: 41-45).

Clinical significance: Metallic and translucent matrices have no influence on clinical performance of Class II composite restorations.

: Dr. Flávio Fernando Demarco, Departament of Operative Dentistry, Dental School, UFPel, Rua Gonçalves Chaves, 457 CEP 96015-560, Pelotas, RS, Brazil. E-: fdemarco@ufpel.edu.br; flavio.demarco@pesquisador.cnpq.br

Influence of light-curing sources on polymerization reaction kinetics of a restorative system

Paulo H. P. D’Alpino, dds, Nádia R. Svizero, dds, José C. Pereira, dds, phd, Frederick A. Rueggeberg, dds, ms, Ricardo M. Carvalho, dds, phd & David H. Pashley, dmd. phd

Abstract: Purpose: To determine the effect of using a variety of commercial light-curing units on polymerization of a dentin-bonding agent (Adper Single Bond) and of a resin composite (Filtek Z250). Methods: Infrared (IR) spectra were obtained kinetically at one scan/second at 2 cm^-1 resolution for a period of 5 minutes and were analyzed for: maximum conversion rate (%/s), time into exposure when maximum rate occurred (seconds), conversion at maximum rate (%), and total conversion (%) at 300 seconds by comparison of aliphatic-to-aromatic absorption IR peak ratios, before and after polymerization. Light units used were: QTH 540 mW/cm² (XL3000); LED 750 mW/cm² (Elipar FreeLight 2); PAC 2,130 mW/cm² (ARC II). Exposure followed manufacturers’ recommendations: dentin bonding agent for 10 seconds, RC for 20 seconds (QTH), and 10 seconds (LED and PAC). Polymerization kinetics was evaluated at the bottom surface (2.5 mm thick) for the resin composite and as a thin film for the dentin bonding agent on the diamond surface of an attenuated total reflectance accessory in the IR spectrometer. Values (n=5) were compared using ANOVA and Tukey’s pairwise post-hoc test: pre-set alpha 0.05. Results: PAC produced the highest total conversion and conversion rate for the resin composite (P< 0.05). Total conversion was lower for dentin bonding adhesive using PAC than with LED or QTH (P< 0.05). LED provided the highest proportion of conversion at the maximum rate with respect to conversion at 300 seconds for both materials. QTH demonstrated the lowest maximum rate value that occurred at a longer time into exposure (P< 0.05). Polymerization kinetic parameters varied greatly between the restorative materials as well as among light-curing unit types when compared to values observed when using a QTH light as control. (Am J Dent 2007;20:46-52).

Clinical significance: Use of different light-curing units to polymerize both the dentin bonding adhesive and the resin composite demonstrated different polymerization parameters that may interfere on the polymerization shrinkage and stress accumulation at the pulpal floor of Class I bonded restorations.

: Dr. José Carlos Pereira, Al. Octávio Pinheiro Brisola, 9-75, Bauru - São Paulo - CEP 17012-901, Brazil. E-: jcper@fob.usp.br

Clinical evaluation of the stain removal efficacy of a novel stannous fluoride and sodium hexametaphosphate dentifrice

Geza TerÉzhalmy, dds, ma, Eros Chaves, dmd, ms, Samer Bsoul, dds, ms, Robert Baker, ms & Tao He, dds, phd

Abstract: Purpose: Recently, sodium hexametaphosphate has been introduced in dentifrice formulations to aid in the control of extrinsic stain. Two independent studies were conducted to evaluate the stain removal efficacy of a novel 0.454% stannous fluoride and sodium hexametaphosphate dentifrice (Crest Pro-Health) relative to a positive control whitening dentifrice (Colgate Total + Whitening) over a 2-week period in a subject population with pre-existing natural extrinsic stain. Methods: These studies were randomized, positive-controlled, parallel groups, double-blind, 2-week trials. Each study involved approximately 30 healthy adults with visible stain of the facial surfaces of the 12 anterior teeth. After baseline examination, subjects were randomly assigned to a treatment and instructed to brush unsupervised with the assigned dentifrice at least twice daily as they normally do. Efficacy was evaluated by modified Lobene examination on anterior teeth at baseline and end-of treatment (Week 2). Results: 59 subjects, 29 in Study 1 and 30 in Study 2, were evaluable and included in the Week 2 analyses. Subjects ranged from 21-68 years of age. In each study, the positive control dentifrice statistically significantly (P< 0.0001) reduced stain scores following 2 weeks of brushing with median reductions of 61.9% and 94.4%. Similarly, the experimental 0.454% stannous fluoride and sodium hexametaphosphate dentifrice statistically significantly (P< 0.0001) reduced stain scores by 61.8% and 96.6% following 2 weeks of brushing. The adjusted mean changes between treatment groups did not differ significantly between the two dentifrice groups (P> 0.70 in each study). Both dentifrices were well tolerated. No subject discontinued treatment due to an adverse event. (Am J Dent 2007;20:53-58).

Clinical significance: This clinical research showed both dentifrices to be safe and effective. The magnitude of stain removal of the novel stannous fluoride and sodium hexametaphosphate dentifrice was comparable to that of the positive control dentifrice. Both dentifrices had a significant effect on reducing extrinsic tooth staining over the 2-week time period.

: Dr. Tao He, Health Care Research Center, Procter & Gamble Company, 8700 Mason-Montgomery Road, Mason, OH 45040, USA. E-: he.t@pg.com

Determination of caries risk at resin composite margins

Norbert Krämer, dmd, phd, Karl-Heinz Kunzelmann, dmd, phd, Franklin García-Godoy, DDS, MS, Ingo Häberlein, phd, Bettina Meier, dmd & Roland Frankenberger, dmd, phd, ficd

Abstract: Purpose: To design an artificial mouth in order to evaluate if a new diagnostic tool (Clinpro Cario Diagnosis) can be used for early detection of secondary caries at resin composite margins in vitro. Methods: 32 intact human third molars received standardized Class-V resin composite restorations (Tetric Ceram bonded with Syntac SC). After storage for 4 weeks at 37°C, teeth were subjected to 5,000 or 10,000 thermocycles (±5°C and ±55°C) and polysiloxane impressions were taken. Streptococcus mutans 10449 (SM) was used in a nutrition medium to initiate a secondary caries process. Daily, the teeth were incubated for 2 x 2.5 hours in SM containing nutrition medium followed by 2 x 9.5 hours incubation in artificial saliva. Teeth were investigated after total incubation periods of 4, 6, and 8 weeks. After the different incubation protocols, the restoration margins were evaluated for infection and secondary caries processes in using Clinpro Cario Diagnosis which measures site-specifically the lactic acid production of SM in response to a sucrose challenge. The color signal was read 5 minutes after removal of the diagnostic impression. After thermocycling and biological load cycling, precision polysiloxane impressions were taken and replicas were investigated under a light microscope for gap widths at enamel and dentin margins. Demineralization was evaluated by fluorescence microscopy in using a special FITC filter. The demineralization depths at the cavity margin were calculated with Xpert for Windows using a pixel distance of 5 µm. Results: After the different thermocycling protocols, no differences in gap widths and demineralization depths were found (P> 0.05). After SM incubation, gap widths and demineralization depths were significantly dependent on SM incubation time and previous number of thermocycles (P< 0.05). Lactic acid formations of SM were detectable by Clinpro Cario Diagnosis at dentin cavosurface margins formed after 6 weeks of incubation with SM (P< 0.05). (Am J Dent 2007;20:59-64).

Clinical significance: Clinpro Cario Diagnosis impressions were able to detect secondary caries processes at resin composite margins in vitro, when gap dimensions were above 40 µm in width.

: Prof. Dr. Norbert Krämer, Department of Paediatric Dentistry, University of Dresden, Fetcherstrasse 74, D-1307 Dresden, Germany. E-: Norbert.kraemer@uniklinikum-dresden.de

From dry bonding to water-wet bonding to ethanol-wet bonding. A review of the interactions between dentin matrix and solvated resins using a macromodel of the hybrid layer

David H. Pashley, dmd, fadm, phd, Franklin R. Tay, bdsc, (hons), fadm, phd, Ricardo M. Carvalho, dds, phd,Frederick A. Rueggeberg, dds, ms, Kelli A. Agee, bs, Marcela Carrilho, dds, phd, Adam Donnelly, bs & Franklin García-Godoy, dds, ms
 

Abstract: Purpose: To review the use of a new resin-dentin bonding model called the macro-hybrid layer, to quantify resin uptake and matrix shrinkage during resin infiltration and solvent evaporation. A secondary purpose was to introduce the concept of ethanol-wet bonding where water-saturated acid-etched dentin is exchanged with ethanol to create ethanol-saturated dentin. Adhesive monomers seem to penetrate ethanol-saturated dentin more thoroughly than water-saturated dentin. (Am J Dent 2007;20:7-21).

Clinical significance: Infiltration of solvated resins in demineralized dentin can be quantitatively followed by using disks of completely demineralized dentin. The results obtained from the macro-hybrid layer can be used to predict how well adhesives can bond to dentin. They indicate ethanol-wet bonding may be superior to water-wet bonding.

: Dr. David H. Pashley, Department of Oral Biology & Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, 1120 15th Street, CL2112, Augusta, GA 30912-1129, USA. E-: dpashley@mail.mcg.edu