Effect of Cervical Lesions on Fracture Resistance and Failure Mode of Maxillary Central Incisors Restored with Fiber Posts and Complete Crowns.

PURPOSE: To investigate the effect of a cervical cavity extending 1 mm apical to the cemento-enamel junction (CEJ) on fracture resistance and failure mode of maxillary central incisors that have been treated endodontically, present with complete and incomplete ferrules, and are restored with and without a fiber post. METHODS AND MATERIALS: 50 intact human maxillary central incisors were divided into five groups (n=10): CG (control group) 6-mm fer-rule height, no cervical cavity, and without post; (CO) 6-mm ferrule height without post, with a cervical cavity (access to root canal and cervical cavity restored with composite resin), cervical cavity; and post with ferrule heights of 1 mm (CP1), 2 mm (CP2), and 6 mm (CP6) restored with fiberglass post and composite resin core. After complete metal crowns were cemented on all specimens, they were subjected to thermal cycling (6000 cycles, 5°C/55°C), followed by immediate testing of fracture resistance. After failure, the specimens were sectioned buccolingually to evaluate and identify the mode of failure. The data were analyzed with an analysis of variance (ANOVA) and the Student-Newman-Keuls multiple comparison tests (α =0.05). RESULTS: A 1-mm ferrule height (CP1) fracture resistance was significantly lower (531±125 N) compared to the 6-mm ferrule height (CP6) (769±175 N) (p<0.05). With respect to the groups with similar residual dentin, with and without a cervical cavity, CG (667±119 N) and CO (668±119 N), the presence of a post (CP6) increased the resistance to fracture, although no statistically significant difference was demonstrated. Partial decementation was observed in all specimens of CG and CP6, in nine of CP1 and CP2, and in three in CO. Root fractures occurred in 23 specimens. The root surface was exposed 2 mm below the CEJ to simulate bone level. Propagation of subosseous cracks occurred in four specimens in CG and CP2, in seven specimens in CP6, in two specimens in CP1, and in six specimens in CO. All were considered catastrophic failures. CONCLUSIONS: Within the limitations of this study it is suggested that, when restoring an endodontically treated maxillary central incisor that has a cervical lesion and needs to be restored with a complete crown, a fiber post is cemented to improve fracture resistance.

The effect of two composite placement techniques on fracture resistance of MOD restorations with various resin composites.

OBJECTIVE: The aim of this in vitro study was to compare the effect of two restorative placement techniques, centripetal incremental technique (CIT) and bulk-fill technique (BT) on the fracture resistance of Class II MOD restorations with various resin composites in molar teeth. MATERIALS AND METHODS: Fifty-six extracted, caries free third molars were prepared with MOD preparations and restored with resin composites. The specimens were divided into two groups by placement technique, centripetal incremental technique (CIT) and bulk-fill technique (BT). Each group was subdivided into four groups according to resin composite: hybrid (Aelite LS), nano-hybrid (Virtuoso Universal), bulk fill (Filtek One Bulk Fill) and the micro-hybrid (Herculite XRV) as the control. RESULTS: Two-way analysis of variance test (ANOVA) followed by the multiple comparison procedure, Student-Newman-Keuls Method showed no a statistically significant difference between placement techniques and fracture resistance of Class II resin composite restorations (P > 0.05). Herculite XRV resisted a significantly higher load before fracture than the other three materials at a 0.05 level of significance, while Virtuoso Universal scored the lowest load. CONCLUSIONS: There was no significant effect of the two placement techniques on the fracture resistance of Class II resin composite restorations CLINICAL SIGNIFICANCE: Resin composite restorations in Class II MODs using a simplified bulk fill placement technique showed no significant difference in fracture resistance with the centripetal technique in molar teeth.

Sealing properties of three luting agents used for complete cast crowns: a bacterial leakage study.

OBJECTIVE: To assess the sealing properties of three different luting materials used for cementation of full cast crowns on extracted human premolars. METHODS: Thirty noncarious human premolars were prepared in a standardized fashion for full cast crown restorations. All margins were placed in dentin. After impressions of the preparations, stone dies were fabricated on which copings were waxed, which were cast in type III alloy using standardized laboratory methods. Teeth were randomly assigned to three groups of 10 samples each (n=10), for which the following cements were used: 1) a resin-modified glass ionomer cement, Rely X Luting Plus (3M ESPE, St Paul, MN, USA); 2) a self-adhesive resin cement, Maxcem Elite (Kerr Corporation, Orange, CA, USA); and 3) a glass ionomer cement, Ketac Cem (3M ESPE), the latter used as control. After cementation the samples were allowed to bench-set for 10 minutes, stored in water at 37°C, subjected to thermal cycling (2000×, between 5°C and 55°C, dwell time 35 seconds), and then stored in sterile phosphate buffer for seven days at 37°C. Subsequently, the occlusal surface was carefully reduced until the dentin was exposed. Finishing on wet sand paper removed the gold flash caused by grinding. After sterilization, the specimens were subjected to bacterial microleakage in a dual chamber apparatus for 60 days. Bacterial leakage was checked daily. Data were analyzed using the Kaplan-Meier survival test. Significant pairwise differences were analyzed using the log-rank test followed by Fisher exact test at a p<0.05 level of significance. RESULTS: Rely X Luting Plus showed the lowest microleakage scores, which statistically differed significantly from Maxcem Elite and Ketac Cem (p<0.05). CONCLUSIONS: Rely X Luting Plus cement displayed significantly lower microleakage scores than a self-adhesive resin-based and conventional glass ionomer cement.

Enterococcus faecalis leakage of root canal sealers: an ex vivo study.

The aim of this ex vivo study was to evaluate bacterial penetration after filling root canals using 3 different techniques. Three experimental groups of 25 teeth each, obturated with lateral-warm-vertical condensation of gutta-percha, Microseal technique and EndoREZ system, respectively, were tested in a split chamber model system using Enterococcus faecalis and monitored for 180 days to determine bacterial penetration. A statistical analysis was performed using the Kaplan-Meier method. Median survival time was 25 days for Microseal system, 41 for lateral-warm-vertical condensation and 81 for EndoREZ®. Significant differences were demonstrated between Microseal and EndoREZ (p less than 0.001) and between Microseal and lateral-warm-vertical condensation technique (p less than 0.05). No statistically significant differences were observed between EndoREZ and lateral-warm-vertical condensation. After 180 days of assessment, 20 percent of the EndoREZ samples resisted bacterial penetration and furthermore, the EndoREZ system has the potential to be a filler system compatible with other currently used systems.

Clinical performance of a bioactive dental luting cement--a prospective clinical pilot study.

OBJECTIVE: To conduct a pilot study determining the clinical efficacy ofa new bioactive dental cement (Ceramir Crown & Bridge) for permanent cementation in fixed prosthodontics. The composition is a hybrid comprised of a calcium aluminate and a glass ionomer. METHODS: This study examined the performance of Ceramir Crown & Bridge after cementation of high-gold alloy and porcelain-fused-to-metal (PFM) single crowns and bridges. A total of 38 crowns and bridge abutments were cemented in 17 patients; 31 were on vital, seven on non-vital teeth. Six were bridges with 14 abutment teeth (12 vital/two non-vital). One fixed splint comprising two abutment teeth was also included in the study. Preparation parameters were recorded, as well as working time, setting time, seating characteristics, and ease of cement removal. Baseline data were collected on dispensing, mixing, and handling of the cement; gingival inflammation index (GI), and a visual analog scale (VAS) and categorical assessment measured pre-cementation sensitivity. Post-cementation parameters were post-cementation sensitivity, categorical and VAS, gingival tissue reaction, marginal integrity, and discoloration. A one-week post-op telephone call recorded subjectively the patients' comfort level. RESULTS: Working time (two minutes) and setting time (four minutes) were well within normal limits. Cement removal was determined to be very easy. Thirteen of 17 patients reported no post-cementation sensitivity after seven days; four reported a low-grade sensitivity. All 17 patients were seen for recall examinations at 30 days and six months. Of the four sensitivity cases, three were related to hyperocclusion, which disappeared spontaneously after adjustment. One case was due to post-cementation pressure from a three-unit bridge, which disappeared without intervention. After six months, no retentive failures were recorded, no sensitivity was subjectively reported, marginal integrity scored 38 alphas, one tooth had a 1 and two teeth a 0.5 GI score. Average VAS score for tooth sensitivity decreased from 7.63 mm at baseline to 0.44 mm at the six-month recall. Average GI score for gingival inflammation decreased from 0.56 at baseline to 0.11 at the six-month recall. CONCLUSION: After six months, Ceramir Crown & Bridge performed favorably as a luting agent for permanent cementation.

One year clinical performance and post-operative sensitivity of a bioactive dental luting cement--a prospective clinical study.

A one-year clinical study was performed on the efficacy of a bioactive dental cement (Ceramir C&B) with calcium aluminate and glass ionomer components. The study was performed on 38 crown and bridge abutments in 17 patients. Preparation parameters were recorded, as well as working-times, setting-times, and other handling characteristics. Baseline data were also recorded for gingival inflammation (GI) and pre-cementation sensitivity. Post-cementation parameters included sensitivity, gingival tissue reactions, marginal integrity and discolorations. All patients were seen for recall examinations at 30 days, and 6 months. For sixteen patients one-year recall data were collected on retention and subjective sensitivity. Fifteen subjects were available for one year clinical examinations. Three independent examiners found the working and setting time of the cement to be well within expected limits and that cement removal was easy. Four patients reported low-grades of immediate post-cementation sensitivity, however, this disappeared after an occlusal adjustment or without intervention within one month. At 12 months no retentive failures were recorded and no subjective sensitivity reported. All crowns were rated in the "Excellent" quality category for marginal integrity. Both GI-scores and scores for tooth sensitivity decreased during the course of the study. One year recall data yielded no incidence of secondary caries and no visible marginal discoloration. The new cement was thus found to perform favorably as a luting agent for permanent cementation.

Influence of surface remodelling using burs on the macro and micro surface morphology of anatomically formed fibre posts.

AIM: To evaluate the effect of modifying preformed fibre-reinforced composite (FRC) endodontic posts on their surface morphology and to determine how this procedure affects the integrity of the posts. SUMMARY: Surfaces of 10 preformed glass-fibre posts (group 1) and carbon-fibre posts (group 2) were compared with those of individually formed glass-fibre posts (group 3). Ten FRC posts were modelled in order to give them a shape as close as possible to the anatomy of oval root canals. Starting from a preformed cylindrical fibre post 2.5 mm in diameter, it was modelled in such a way as to passively occupy the entire post-space length, using a cast previously created as a guide. Microscopic analyses (optical stereomicroscope and scanning electron microscope) of the post surfaces revealed similar features in all three groups. All posts had regular surfaces after cutting with a diamond bur. Smear layer mainly attributable to the cutting procedures covered the cut surface of some specimens. In conclusion, modulation of a fibre post using a diamond-coated bur did not show a loss of integrity of the post. *Because of the importance of micromechanical retention, the surface integrity of fibre posts may be important for adhesion between post and composite resin. *Modification of a fibre post using a diamond-coated bur did not damage the surface integrity of the posts. *Fibre posts can be ground to a different shape without losing their surface integrity, resulting in posts with a surface that is not visibly different from unmodified commercially available fibre posts.

Retreatment efficacy of hand versus automated instrumentation in oval-shaped root canals: an ex vivo study.

AIM: To compare the efficacy of hand versus automated instrumentation when retreating oval-shaped root canals. METHODOLOGY: Sixty human premolars with single oval canals were instrumented and filled with gutta-percha and sealer and divided into three groups (n = 20)--group 1: ProFile .04 taper rotary instruments; group 2: Anatomic Endodontic Technology (AET), and group 3: manual instrumentation with Hedström files. The teeth were split longitudinally and gutta-percha/sealer remnants in the coronal, middle and apical thirds were assessed with light microscopy. The mean percentage of gutta-percha/sealer remnants for each group was calculated and statistically analysed for significance using an ANOVA repeated measures (P < 0.001) and Tukey's multiple comparison test. The time required for retreatment was analysed using a one-way ANOVA and Tukey's test (P < 0.001). RESULTS: Overall, 10-18% of the canal walls were covered with gutta-percha/sealer remnants after preparation using any technique. Statistical analysis demonstrated that the mean values for remnants of filling material in the ProFile group were significantly higher than for the other groups (P < 0.001), except in the apical third where no significant difference occurred. In all groups, the mean values in the middle third were higher than the coronal and apical thirds. The retreatment time for ProFile and AET was significantly shorter compared to manual instrumentation with Hedström files (P < 0.001). CONCLUSIONS: Under the experimental conditions, AET instruments and manual instrumentation with Hedström files resulted in cleaner canals. However, completely clean root canal walls were not produced with any of the techniques investigated.

Effectiveness in cleaning oval-shaped root canals using Anatomic Endodontic Technology, ProFile and manual instrumentation: a scanning electron microscopic study.

AIM: To compare in vitro the cleanliness of root canal walls in oval-shaped root canals following automated or manual instrumentation. METHODOLOGY: Forty-five oval-shaped single-rooted maxillary and mandibular premolars with straight canals were divided into three groups of 15. Automated canal preparation was performed using Anatomic Endodontic Technology (AET, group 1) and the ProFile system (group 2). Manual instrumentation (group 3) was performed with K-Flexofiles. Irrigation was performed using alternately 5.25% NaOCl and 17% EDTA, followed by rinsing with saline. The roots were split longitudinally into halves and the canals examined at x200 and x400 in a scanning electron microscope. The presence of debris and smear layer was recorded at distances of 1, 5 and 10 mm from the working length using a three-step scoring scale and a 300 mum square grid. Mean scores for debris and smear layer were calculated and statistically analysed for significance (P < 0.05) between and within groups, using the Kruskal-Wallis nonparametric anova and Dunn's tests. RESULTS: At 1, 5 and 10-mm levels the root canals prepared with AET had significantly less surface debris and smear layer on the canal walls compared with canals prepared with ProFile or manual instrumentation. For all three groups significantly lower mean smear layer scores (P < 0.05) were recorded at 5 and 10-mm levels compared with the 1 mm level. Significantly lower mean debris scores (P < 0.05) were also recorded at 5 and 10-mm levels for the AET group whereas no significant differences were found between the three levels for the ProFile and manual instrumentation groups. CONCLUSIONS: Although better instrumentation scores were obtained in canals prepared with AET, complete cleanliness was not achieved by any of the techniques and instruments investigated.

Volumetric polymerisation shrinkage of different dental restorative materials.

STATEMENT OF PROBLEM: Polymerisation shrinkage is a critical limitation of dental resins and may contribute to micro leakage. PURPOSE: The purpose of this study is to record and compare volumetric changes of various dental composites and compomers, exposed for 40 seconds to a commercial halogen light source. MATERIAL AND METHODS: Eleven light-polymerised composites and compomers were evaluated using a dilatometer that recorded the polymerisation shrinkage every 0.5 second. The mercury column pressure was measured electronically with a pressure-sensitive transducer, and the data recorded and stored in a computer. The computer also recorded the temperature, controlled the light-source and displayed the data in graphic format. Every material was tested ten times. The data were analysed by means of an ANOVA (P < 0.05). RESULTS: A high rate of shrinkage occurred for all materials in the first ten seconds of polymerisation. Surefil showed the lowest rate while TPH displayed the highest. Of the higher filled materials, Surefil (0.96%) showed the least shrinkage, followed by Z250 (0.99%), Dyract AP (1.18%), Herculite (1.27%), Compoglass (1.32%), Amelogen (1.34%) and TPH-Spectrum (1.6%). Overall, the flowable materials exhibited significantly more shrinkage (P < 0.05). For this group Compoglass Flow (2.3%) showed the least shrinkage followed by Filtec Flow (2.31%). Permaflo (3.6%) exhibited the most shrinkage followed by Dyract Flow (3%). CONCLUSION: Within the limitations of this study, it is concluded that significant differences exist among the polymerisation shrinkage of the most resins tested. An increase in the filler content of a material significantly lessens the polymerisation shrinkage while an increase in the monomer concentration causes significantly more polymerisation shrinkage. CLINICAL SIGNIFICANCE: The more flowable a composite material becomes, the more the restoration will shrink. Clinicians should take this into account when they decide on cavity design and materials to use.

Pulp histology after Er:YAG laser cavity preparation in subhuman primates--a pilot study.

UNLABELLED: The aim of the study was to make a direct comparison of the pulpal effects of laser and turbine preparations in subhuman primates. One female baboon (Papio Ursinus ursinus), weighing 15 kg, was used. General anaesthesia was administered (ketamine 100 mg/ml/kg body weight) and maintained with acepromazine (10 mg/ml/kg body weight). Class V cavities were prepared buccally in a total of 28 teeth (7 in each quadrant). Teeth in the upper right and lower left quadrants were prepared using a conventional 330 carbide bur in a high-speed fibre-optic handpiece with copious water spray. Teeth in the upper left and lower right quadrants were prepared using an Er:YAG laser drill (Fotona Twinlight, Llubljana, Slovenia) delivering 500 mJ at a pulse rate of 10 Hz and a wavelength of 2940 nm. The animal was sacrificed after 25 days. After general anaesthesia as described before, perfusion fixation of the head was accomplished with 10% neutral buffered formalin, pumped through a catheter inserted into the left carotid artery. The jaws were removed and, using a 330 carbide bur in a high speed handpiece, a continuous groove was cut through the bone and the roots at the level of the middle third of all the roots to promote thorough fixation of pulpal tissue. Decalcification and grading of the severity of the pulpal responses were conducted according to standard procedures. RESULTS: Owing to procedural errors seven teeth, FDI numbers 23, 24, 31, 34, 35, 44 and 45, had to be eliminated. The turbine-prepared teeth (N = 11) had a mean remaining dentine thickness (RDT) of 0.77 mm (SD = 0.42) and the laser-prepared teeth (N = 10) had a mean RDT of 0.81 mm (SD = 0.60). All pulps appeared normal except in one turbine-prepared tooth (12 with RDT = 0.20) and one laser-prepared tooth (27 with RDT = 0.30, where irreversible damage was caused. The only other deviations from normal were seen in the laser-treated 41 (RDT = 0.69) and the turbine-treated 36 (RDT = 0.77) where moderate hyperaemia was seen. Within the limitations of this study it can be concluded that there is no significant difference between dental pulp of teeth where Class V cavities were prepared with an Er:YAG laser drill compared with those prepared with a standard turbine drill.

Pulp capping with a modified bioglass formula (#A68-modified).

PURPOSE: To evaluate a modified Bioglass (Formula #68 (MBF68) when used as a pulp capping agent. MATERIALS AND METHODS: After exposure, the pulps were contaminated with saliva for 60s, rinsed, dried and treated with Consepsis, acting as a hemostatic and bactericidal agent. After drying the Consepsis, the MFB68, having been pre-mixed in sterile saline, was carefully deposited over the pulp exposure, covered with polycarboxylate cement and restored with the ProBond bonding resin system. A calcium hydroxide group was used as control. RESULTS: There was no evidence of mummification, the incidence of properly positioned dentin bridge formation was higher and the incidence of extruded dentin bridge formation was reduced.

Effect of carbamide peroxide bleaching agents on the physical properties and chemical composition of enamel.

PURPOSE: To evaluate the effect of two commercially available carbamide peroxides bleaching agents, Opalescence and Nite-White, in concentrations of 10, 15 and 16%, on enamel. MATERIALS AND METHODS: Vickers hardness measurements (VH) were made at the surface and 110 microns below the surface on human enamel samples that were treated for 5 or 10 days, 6 hrs/day. Furthermore, infrared spectrophotometry (IR), Fourier transform infrared spectrophotometer (FTIR) and X-ray diffraction (XRD) measurements were performed after the VH measurements were completed. RESULTS: Using a one-way ANOVA, statistically significant differences in VH could be established between surface and subsurface VH values. For all groups, including the control group, the surface VH values were statistically significantly higher than subsurface VH. IR, FTIR and XRD established a change from hydroxyapatite to primary calcium ortho phosphate [Ca(H2PO4)2] for all experimental groups except for 10% Opalescense tested for 5 or 10 days.

Retention of parallel-sided titanium posts cemented with six luting agents: an in vitro study.

PURPOSE: This in vitro study compared the effectiveness of 6 luting systems on the retention of prefabricated titanium posts. MATERIAL AND METHODS: A total of 120 single-rooted teeth were sectioned at the cementoenamel junction and treated endodontically. Roots were mounted in copper cylinders, and prefabricated, parallel-sided titanium posts were cemented according to the manufacturer's instructions. Two resin-ionomer hybrid cements and 2 resin cements were tested with corresponding dentin bonding agents. A glass ionomer cement was also tested, and zinc-phosphate cement served as the control. Samples were tested in an Instron universal testing machine to catastrophic tensile failure. RESULTS: Advance cement with Prime and Bond systems was found to be statistically more retentive than all other groups tested (P < .05). Cement It with Bond It and Permalute with Permalute Primers A and B systems demonstrated significantly greater retention than Ketac Cem cement, Resinomer with One-Step system and zinc-phosphate cement (P < .05). There was no statistically significant difference among Ketac Cem cement, Resinomer with One-Step system, and zinc-phosphate cement.

The disastrous effects of the "total etch" technique in vital pulp capping in primates.

PURPOSE: To determine by means of a histopathological study in sub-human primates whether etching of an exposed pulp (the "Total Etch" technique) followed by capping with dentin bonding agents is a viable clinical treatment modality. MATERIALS AND METHODS: In six sub-human primates, 147 Class V preparations were made for five experimental and two control groups. After exposing the pulps, the preparations were intentionally contaminated, rinsed, dried and then disinfected with a 2% chlorhexidine solution for 60 s. In the five experimental groups, the entire preparation including the exposed pulp was etched with a 35% phosphoric acid gel, which was rinsed after 20 s. This was followed by a second application of chlorhexidine. In Groups 1-3, All Bond 2, ProBond and Permagen A&B dentin bonding agents were applied as pulp capping materials. In Group 4, a light-cured calcium hydroxide was tested while Group 5 was treated with a chemically-cured calcium hydroxide. Groups 6 and 7, the controls, were also contaminated, rinsed, dried and disinfected. After the exposed pulps had been protected with a chemically-cured calcium hydroxide (Group 6) or a light-cured calcium hydroxide (Group 7) the preparations were etched and restored with a bonded resin composite. The effect of the above described treatments were evaluated at 5, 25 and 75 days. After sacrifice and routine histological preparation, histological sections were graded among other parameters for inflammatory response, bridge formation, maintenance of vitality, presence of dentin chips and evidence of microleakage microorganisms. RESULTS: The 2% chlorhexidine applied immediately after exposure was an effective hemostatic agent. After subsequent etching, the hemostatic effectiveness was greatly reduced. Exposure size for all seven groups ranged from 0.13-1.55 mm. The average at 5, 25 and 75 days measured 0.74, 0.66 and 0.77 mm, respectively. In the five experimental groups, the 25- and 75-day groups had a total of 68 teeth of which 24 (35%) became non-vital and 23 (33%) teeth demonstrated bridge formation. In the three experimental groups using a bonding agent, the 25- and 75-day groups had a total of 40 teeth of which 18 (45%) became non-vital and 10 (25%) exhibited bridge formation. In the "No Etch" control groups, the 25- and 75-day groups had 28 teeth of which two (7%) became non-vital and 23 (82%) exhibited bridge formation. Microorganisms were found in a large percentage of all groups, although their numbers were few. However, they were present in vital and non-vital teeth, in the presence and absence of bridge formation and had no direct bearing on the success or failure of the pulp capping procedure.

Adherence of "stuck" restorations to demineralized dentin following use of experimental primers.

PURPOSE: This in vivo study histopathologically evaluated the biocompatibility of four self-conditioning dentinal primer formulas in four bonding systems and evaluated the pulpal responses of the self-conditioning dentinal bonding systems for Class V tooth preparations in primates. MATERIAL AND METHODS: The basic formula consisted of proprietary carboxylic diacid monomer, dipentaerythritol pentaacrylate phosphoric acid ester, acetone, and ethanol that was used alone or mixed with other commercial priming agents. After application of primers, Prisma Universal Bond 3 was selected to restore the cavity preparations. RESULTS: All systems were judged histopathologically biocompatible. "Stuck" restorations that were resistant to acid demineralization necessary for processing of histologic slides, occurred more frequently with intact smear layers and increasing use of dehydrating agents. CONCLUSIONS: Tests should be performed to determine whether "stuck" restorations in in vivo studies that maintain dentin-pulpal relationships can support in vitro shear bond strength tests.

Significance of pulpal pressure during clinical bonding procedures.

PURPOSE: To determine whether pulpal pressure in vital teeth plays a significant role in dentin bonding procedures. MATERIALS AND METHODS: Half the teeth in three baboons received root canal treatment thus eliminating pulpal pressure. All teeth were then prepared on the buccal surface with a diamond wheel to create flat surfaces into dentin, measuring at least 4 mm in diameter. Dentin bonding systems from two manufacturers were applied. Using a Bencor tensile nozzle freehand, 3.5 mm diameter composite buttons were bonded to the prepared surfaces. The animals were sacrificed 24 hours later, the teeth removed and mounted in specimen rings, using the same Bencor tensile nozzle for proper axial alignment. The composite buttons were tested for shear bond strength in a tensometer. RESULTS: The results showed no statistically significant difference between the two materials tested, furthermore there was no difference in SBS between materials bonded to vital or non-vital teeth. After completion of the tests, 20 teeth (10 for each dentin bonding system) were prepared according to standard laboratory procedures for a dentin bond strength test using the Bencor Multi-T system. The values obtained were higher, but again there was no statistically significant difference between the two systems.

Retentive properties and film thickness of 18 luting agents and systems.

In the past, retention of castings depended on mechanical interlocking or adhesion to enamel and dentin by means of chelation in the case of some cements. Some new luting agents adhere to metal and tooth structure. The era of bonded casts for crowns and bridges has arrived through a combination of dentin primers and luting agents that bond to enamel, dentin, and precious and nonprecious metals. For a few systems, the retentive forces (in an otherwise nonretentive experimental design) more often than not exceeded tooth strength.