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PubMed2004

Influence of substrate, shape, and thickness on microtensile specimens' structural integrity and their measured bond strengths.

OBJECTIVES: To verify whether substrate, shape, or thickness of microtensile specimens have a significant influence on their measured bond strength. METHODS: Sixty-four extracted molars provided microtensile specimens, which were prepared on enamel and dentin, in different shapes and thicknesses. The teeth were randomly divided into 16 groups (n = 4). Groups 1-8 included hourglass-shaped specimens. In Groups 1-4 specimens were prepared from enamel and in a thickness at the bonding interface of 0.5 mm x 0.5 mm, 1 mm x 1 mm, 1.5 mm x 1.5 mm, and 2 mm x 2 mm, respectively. In these same thicknesses, hourglasses were trimmed in Groups 5-8, but the specimens were prepared from dentin. Groups 9-16 included specimens obtained following the non-trimming technique. Groups 9-12 provided enamel sticks in the four evaluated thicknesses. In these same thicknesses and shape but from dentin were cut the specimens of Groups 13-16. Two specimens from each group were viewed using a scanning electron microscope. On the other ones, microtensile bond strength was measured and the values were statistically analyzed. RESULTS: Substrate, shape, and thickness of the specimens had a significant effect on their recorded bond strength (p < 0.05). Higher bond strength values were recorded by dentin versus enamel specimens and by sticks versus hourglasses. Also, bond strength decreased as specimen thickness increased. SEM analysis revealed that the trimmed specimens, especially if from enamel, often exhibited lines of fracture in the area of action of the bur. SIGNIFICANCE: It seems advisable to avoid the trimming action particularly on enamel specimens. If the hourglass shape is preferred, the cross-sectional area should not exceed 1 mm x 1 mm.

Analysis of Variance↗
PubMed2001

The effect of luting media on the fracture resistance of a flame sprayed all-ceramic crown.

OBJECTIVES: This in vitro study investigated the effect of selected luting media on the fracture resistance of a flame-sprayed all-ceramic crown. METHODS: Three groups of 10 human upper premolar teeth were prepared for crowning using a standardised technique. Flame sprayed crowns were fabricated and cemented onto the preparations using zinc phosphate (ZPC), glass polyalkenoate (GPC) or composite luting cement (CLC). During crown seating, a pressure perfusion system simulated pulpal fluid outflow equivalent to 300mm of H2O. Compressive fracture resistance was determined for each group using a Universal Testing Machine with a crosshead speed of 1mm min(-1). A group of unrestored teeth acted as a control. RESULTS: The fracture resistance of the groups ranked as follows: ZPC>CLC>>GPC=unrestored teeth. The difference between the fracture resistance of ZPC and CLC groups and the control group was statistically significant. The mode of fracture between the luted crowns and natural crowns was markedly different. CONCLUSIONS: When tested in compression, a new, flame-sprayed all-ceramic crown, when luted in place using ZPC, GPC or CLC, could produce strengths comparable to or greater than natural unrestored teeth. The luting agent used significantly affected the recorded fracture loads.

Analysis of Variance↗
PubMedDate not supplied

The effect of sulcular width on the linear accuracy of impression materials in the presence of an undercut.

PURPOSE: This study examined the effect of gingival sulcular width, in the presence of an undercut, on the accuracy of dies poured from impressions made with different impression materials. MATERIALS AND METHODS: Three polyvinyl siloxanes (Examix, Elite, and Express), one polyether (Permadyne), and one polysulfide (Permlastic) were used to make impressions of six metal dies. The dies were machined to simulate teeth with a chamfer preparation, root convergence, and sulci of varying widths (0.10 to 0.40 mm). The impressions were poured with type IV stone, and the resulting dies were measured under a traveling microscope at the level of the finish line. The distortion of each die was calculated. RESULTS: The distortion ranged from 0.01% to 0.89%. All materials showed similar behavior: At the narrowest sulcular width (0.10 mm), the distortion was considerably larger (0.43% to 0.89%) than at the wider sulci (up to 0.20% in most cases). Examix (polyvinyl siloxane), Permlastic (polysulfide), and Permadyne (polyether) gave the most accurate dies for sulci 0.15 mm and wider. Express (polyvinyl siloxane) showed greater deformation than other materials in most sulcular widths under the conditions of this study. CONCLUSION: Accurate impressions can be expected in sulci > or = 0.15 mm in width at the level of the finish line coronal to an undercut. Impressions with 0.10-mm sulci widths are not predictable. The physical properties of the impression materials used cannot be anticipated based on their chemical group.

Analysis of Variance↗
PubMed2000

Predictions of cement microfracture under crowns using 3D-FEA.

PURPOSE: The objective of this research study was to test the effects of (1) crown margin type, (2) cement type, (3) cement thickness, (4) loading direction, and (5) loading magnitude on stress levels and distributions within luting cement that might lead to cement microfracture using three-dimensional Finite Element Analysis techniques. MATERIALS AND METHODS: Thirty-two three-dimensional computer models, as well as models for standards, were generated for a mandibular first premolar. Crown preparations exhibited shoulder or chamfer margin configurations, and zinc phosphate, zinc polycarboxylate, glass ionomer, and resin cements were used in thicknesses of 25 or 100 microm. Modeled crowns were loaded axially or obliquely at 10 and 100 MPa. Areas and levels of stress concentrations within the cement were determined. RESULTS: Stresses in the cement were low for all situations except 100 MPa oblique stressing. Stresses at the margins of crowns with chamfer marginal configuration were higher than those with shoulder margins. Stresses under oblique stressing were 10 to 150 times higher than under axial stressing. Except for Zn phosphate cement, cement thickness minimally affected stress levels and distributions. Greater stresses were found in cements with the greater Young's modulus. CONCLUSIONS: Although the chamfer margin design could lead to greater stresses near the margins that places the cement at risk for microfracture and possible crown failure, glass-ionomer and composite resin cements have more favorable mechanical properties for resisting microfracture.

Bicuspid↗
PubMed2006

A three-dimensional evaluation of a laser scanner and a touch-probe scanner.

STATEMENT OF PROBLEM: The fit of a dental restoration depends on quality throughout the entire manufacturing process. There is difficulty in assessing the surface topography of an object with a complex form, such as teeth, since there is no exact reference form. PURPOSE: The purpose of this study was to determine the repeatability and relative accuracy of 2 dental surface digitization devices. A computer-aided design (CAD) technique was used for evaluation to calculate and present the deviations 3-dimensionally. MATERIAL AND METHODS: Ten dies of teeth prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). The surfaces were digitized 3 times each with an optical or mechanical digitizer. The number of points in the point clouds from each reading were calculated and used as the CAD reference model (CRM). Alignments were performed by registration software that works by minimizing a distance criterion. In color-difference maps, the distribution of the discrepancies between the surfaces in the CRM and the 3-dimensional surface models was identified and located. RESULTS: The repeatability of both scanners was within 10 microm, based on SD and absolute mean values. The qualitative evaluation resulted in an even distribution of the deviations in the optical digitizer, whereas the dominating part of the surfaces in the mechanical digitizer showed no deviations. The relative accuracy of the 2 surface digitization devices was within +/- 6 microm, based on median values. CONCLUSION: The repeatability of the optical digitizer was comparable with the mechanical digitization device, and the relative accuracy was similar.

Computer-Aided Design↗
PubMed2004

Parameters affecting retentive force of conus crowns.

The aim of this study was to determine the values of the retentive forces of the telescopic crowns. At the first step of the study, the samples having different heights and angles were compared in relation to retentive force. At the second step, the samples were subjected to removal procedures having a pre-determined speed, force and number. The obtained retention values were compared. Ninety dies were prepared in order to measure the retention of the conus crowns. The removal tests were performed with the insertion/separation device. The speed of the test device was 100 cm min(-1) providing the placement of the pieces with 5 kgf in 100, 200, 300, 500, 1000, 5000 and 10 000 cycles. The mean of the retention values of the changes of the angles were found to be statistically different (P < 0.01). According to the results of the variant analysis, the differences in the changes of the height were statistically significant (P < 0.01). The differences between the changes of the number of procedures of all groups were statistically significant (P < 0.01). The number of procedures, height and angle interactions were statistically insignificant (P = 0.758). According to the results of this study, the effect of the angle and height factors in terms of retention among the groups were not independent of each other. In equal angles, as the height increased, increased retention measurements were obtained. In more acute angles, the increase in retention was more obvious. It was also found that an accessory device was necessary to maintain retention capabilities after a long-term use.

Crowns↗
PubMed2002

A six-canal maxillary first molar: case report.

AIM: The aim of this case report is to describe an unusual six-canal maxillary first molar tooth. CASE REPORT: The maxillary left first molar of a young African-American male was treated as an emergency at the first visit. At the second visit, the five canals (MB1 and 2, Pal1 and 2 and DB) were easily identified at high magnification of 16-25 under an operating microscope. The canals were then instrumented and filled using the Microseal technique. A careful radiographic examination of the final fill indicated that there was a third canal in the palatal root as suggested by a slight extrusion of the filling material between the two canals. At the third visit, the fillings of the palatal canals were removed and the apical 4mm was re-examined. The existence of a third palatal canal exiting between the two apices was verified and subsequently instrumented and obturated. KEY LEARNING POINTS: It should be assumed that all molar teeth have more than the traditionally expected three canals. The location of root canals should be identified at high magnification under the microscope. Careful radiographic re-examination of the fillings should be done in order to identify possibly missed canals.

Adult↗
PubMedDate not supplied

Effect of seating force, margin design, and cement on marginal seal and retention of complete metal crowns.

PURPOSE: The purpose of this study was to determine the marginal discrepancy and retention of silver-palladium crowns cemented with zinc phosphate (Phosphacap) and glass-ionomer cement (Fuji Cap 1) using different seating forces on preparations with various margin designs. MATERIALS AND METHODS: Crown preparations with three finish lines--chamfer, shoulder, and shoulder with a 45-degree bevel--were sequentially prepared on a dentoform premolar. A metal die for each of the three finish lines was constructed. Complete metal crowns were fabricated for each metal die using a silver-palladium alloy. Three different seating forces--25, 100, and 300 N--were used to load the crowns until initial set of the cement. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using a digimatic indicator. Retention was determined by measuring the tensile strength using the Lloyd universal testing machine. RESULTS: The higher seating forces produced better crown seating but had no significant effect on crown retention. The shoulder and shoulder with bevel finish lines provided better crown retention than the chamfer. Glass-ionomer cement provided greater crown retention than zinc phosphate cement. No significant correlation between marginal seating and crown retention was revealed using a Pearson analysis. CONCLUSION: Marginal seal was not influenced by either margin design or type of luting cement, but was improved with higher seating force. Crown retention was affected by the margin finish line and the luting agent.

Analysis of Variance↗
PubMed1997

The effect of seating force and die spacing on pulpward cementation pressure transmission: a laboratory study.

Pulpward pressure transmission during crown cementation occurs via the dentinal tubules. The present study investigated the effect of crown seating forces and the effect of increasing the die spacing on pulpward pressure transmission. Twenty upper premolars were prepared with 1 mm shoulder margins for non-precious metal full crowns. A 0-104 kPa pressure transducer (Mediamate EA, Data Instruments, Baltimore, MD, USA) was connected, via the sectioned root of the premolar, to the pulp chamber which was perfused with saline at 83 kPa driven by nitrogen gas, for two hours prior to cementation. Crowns with 2 or 6 layers of die-spacing were seated with 25 N or 100 N force using zinc-phosphate cement. The pressure transducer was connected to a Wheatstone bridge (Measurements Group, Instruments Division) and the extent of crown seating and output from the pressure transducer was recorded. Results indicate that 25 N seating force produced a lower mean pulpward pressure (41 +/- 54 Pa) compared to the 100 N seating force (251 +/- 276 Pa). Seating was significantly improved with 6 layers of die-spacing (seating discrepancy 18 +/- 12 mm) compared with 2 layers (139 +/- 111 mm). It is concluded that a higher seating force increases pulpward pressure transmission. Increasing die spacing improved crown seating but did not affect the amount of pressure transmitted.

Adolescent↗
PubMed2003

[Gingival risks of fixed prostheses at the Institute of Odontology and Stomatology of Dakar (I.O.S.)].

The realisation of a bridgework involves a direct action on the gingival marginal edge. It is submitted to peremptoriness of execution that one of the objectives is to respect the periodontium with a great rigour. In the opposite case it can become a greater aggression agent, source of prosthetic failures we carried out this report in order to evaluate in the framework of a pedagogic operational programme of crown and bridge prosthesis, the superficial periodontal risks linked to the preparation of the abutment teeth and to the prosthetic chain. We examined a randomised sample of 50 patients chosen from the Dakar LOS prosthetic consultation. On the periodontium initially sound we noted inflammatory lesions of the superficial periodontium from the beginning to the end of the treatment we used the Russel periodontal index. The whole individual scores summarised on a collective chart have been submitted to the statistical analysis of the independence by using the chi-square test. The population consulting in bridge work at the Dakar LOS is relatively young, 33 years in a average with a sex ratio of 1.17 and it shows a moderate (60% of the cases) and severe periodontal seizure (40% of the cases) dealing significantly with the type of prosthesis and the axial and occlusal morphology of the prosthesis pieces. This study shows that prosthesis rehabilitation in the frame work of a clinical training at the Dakar I.O.S. includes relatively high risks of periodontium aggression that we would minimise by setting more correctly the indications of the bridge work and by bringing more rigour to the record and the postpone of the patients occlusion in the laboratory conception of the prosthesis pieces.

Adult↗
PubMed1997

Effect of provisional cements on the bond strength of various adhesive bonding systems on dentine.

Temporization of prepared teeth is needed for protection of the pulp and the restoration of the patients' aesthetic and functional needs. When zinc-oxyphosphate cement is used, eugenol-containing provisional cements are preferred because of their sedative effect to the pulp and because of their acceptable compressive strength. However, prior to definitive adhesive cementation with composite luting resins and dentine bonding agents the use of eugenol-containing provisional cements has to be considered critical because eugenol severely disturbs the polymerization of resinous materials. The purpose of this study was to compare shear bond strength values of various adhesive luting systems on dentine which had been in contact with various provisional cements prior to dentine bonding. The results show that the provisional cements which were used considerably decreased some of the bond strength values of the dentine bonding systems tested. Freegenol and Fermit, however, seem to have beneficial effects on the SBS values of Syntac and ART Bond. The only bonding system which produces acceptably high average SBS values with a eugenol-containing provisional cement was P-Bond.

Adhesives↗
PubMed2000

The effect of venting on pulpward pressure transmission and seating on crown cementation: a laboratory study.

Measurable hydraulic forces towards the pulp chamber can occur whilst cementing a crown. This study investigated the effect of crown venting and the use of two different seating forces (100 and 2. 5 N) on pulpward pressure transmission. Forty single-rooted premolar teeth were collected from patients requiring extractions for orthodontic reasons. A standardized crown preparation was made and impressions taken to construct individual base-metal alloy crowns. The teeth were divided into four groups based on the type of crown (vented or non-vented) and force used (100 or 2.5 N). The teeth mounted on a specially constructed stand and connected to a 0-104 kPa pressure transducer. The pulp chamber was perfused with saline driven by nitrogen gas at 83 kPa for up to 2 h until a steady state perfusion rate was achieved. Crowns were cemented to the teeth on a uniaxial seating device using zinc phosphate cement. Simultaneous recordings of both pressure pulse and seating discrepancies were recorded. The 40-fold increase in seating force from 2.5 to 100 N resulted in a significant increase (P<0.001) in pulpward pressure in both vented and non-vented crowns. Seating was also significantly improved for the vented crowns regardless of which force was used. Venting had no significant effect on pulpward pressure transmission. It was concluded that a significant relationship existed between seating force and pulpward pressure transmission. Venting improved crown seating but did not have a demonstrable effect on pulpward pressure transmission.

Analysis of Variance↗
PubMedDate not supplied

In vitro fitting accuracy of copy-milled alumina cores and all-ceramic crowns.

PURPOSE: The purpose of this study was to evaluate the marginal and internal fit of alumina cores and all-ceramic crowns in a new preparation design for abutment teeth devised for copy milling. MATERIALS AND METHODS: Using conventional dies and dies from the new type of preparation design, 20 alumina cores were produced by copy milling, 10 cores in each die type. Also using the new type of die, another 10 final crowns were fabricated. Each of the 30 specimens was returned to its original die and embedded in epoxy resin. Each specimen was then sectioned labiolingually and measured for gaps at the margin, in the central area, and at the incisal edge. RESULTS: The alumina cores fabricated using the new type of die had mean gaps of 30 to 40 microns at the margins of the labial and lingual sides, which was significantly smaller than the gaps (67 to 130 microns) found in the alumina cores produced with the conventional type of die. The final crowns had mean gaps of 44 to 63 microns at the margins and on the inner surfaces. There was no significant difference in the gaps between the alumina cores produced using the new type of die and those found in the final crowns. CONCLUSION: The new type of die was effective in allowing the fabrication of all-ceramic crowns that provide excellent marginal and internal fit by copy milling.

Adhesives↗
PubMed2006

Mechanical properties and bond strength of dual-cure resin composites to root canal dentin.

OBJECTIVES: To evaluate the regional mechanical properties of dual-cure resin composites and their regional bond strengths to root canal dentin. METHODS: One of the following dual-cure resin composites was placed in artificial post spaces: Unifil Core (UC), Clearfil DC Core (DC), Build-It FR (BI), Clearfil DC Core-automix (DCA), and photo-cured for 60s. After 24h storage, each specimen was serially sliced to harvest eight hour-glass shaped specimens for measurement of regional ultimate tensile strength (UTS), and the remaining eight semi-circular slabs were polished for the measurement of Knoop Hardness Number (KHN). For the microtensile bond strength (muTBS) test, post cavities were prepared in human premolar roots, and the cavity surfaces treated with Clearfil SE Bond and photo-cured for 10s. The post spaces were then filled with one of the above resin composites and photo-cured for 60s. After 24h storage, each specimen was serially sliced into 8, 0.6x0.6 mm-thick beams for the muTBS test. The data were divided into coronal and apical regions and analyzed using ANOVA and post hoc test (alpha=0.05). RESULTS: UTS and KHN were affected by the type of dual-cure resin composite and region (p<0.0001). There was no relationship between UTS and KHN for each material. The auto-mix type of resin composite possessed superior UTS to that of the hand-mix type. muTBS among the four composite materials were not significantly different at both apical and coronal regions (p>0.05). Regional differences in bond strengths were found for all materials (p<0.05). SIGNIFICANCE: The UTS and KHN of the dual-cure resin composites varied among each material, however, differences in the mechanical properties of the resin core materials did not affect their adhesion to root canal dentin.

Composite Resins↗
PubMed2003

[The effect of rehabilitation of flared root canal on the fracture resistance of root and post-core system].

OBJECTIVE: To assess the effect of rehabilitation of flared root canal on the fracture resistance of root and post-core system. METHODS: Thirty-two simulated tooth roots made of polymethyl methacrylate were divided into 4 groups, including the normal root canal group and 3 flared root canal groups. One flared root canal group was rehabilitated by light-cared composite, another group was rehabilitated by amalgam, and the third flared root conal group was not treated. Casting post and core restored every simulated tooth root. Each specimen was embedded in acrylic resin and then fixed in a special jig on the universal load-testing machine. A compressive load was applied at a 90-degree angle to the long axis of the core until fracture, at a crosshead speed of 1 mm/min; the maximum of load was recorded. RESULTS: The means of load in normal root canal group, light-cared composite rehabilitated group, amalgam rehabilitated group, not treated group were 202.92 N, 194.60 N, 146.89 N, 142.09 N. It was shown that the load of normal root canal group is significantly greater than the load of not-treated group (P < 0.01); the light-cared composite rehabilitated group is significantly stronger than the not-treated group (P < 0.01), but there is no significant difference between the light-cared composite rehabilitated group and normal root canal group, and no significant difference between the amalgam rehabilitated group and not-treated group (P > 0.05). CONCLUSION: The rehabilitation of flared root canal using suitable material not only changes the shape of root canal, but also increases the fracture resistance of root canal because of its thicker and stronger root canal wall which obviously improves the fracture resistance of post and core.

Acrylic Resins↗
PubMed2001

Metal-free inlay-retained fixed partial dentures.

OBJECTIVE: The treatment procedures used in conjunction with two different metal-free restorative systems are illustrated on the basis of clinical examples. In addition, a report on the initial clinical findings is provided. METHOD AND MATERIALS: Metal-free restorative materials are opening doors to new preparation methods because of their close link to the adhesive cementation technique. As a result of the developments over the past few years, various metal-free systems that can be used to fabricate short-span fixed partial dentures (FPD) are now available. Certain guidelines, however, must be observed in the process. Because of their minimal invasiveness, inlay-retained FPDs offer an interesting solution in cases where the residual dentition exhibits low caries activity. Since the beginning of 1997, a total of 23 metal-free inlay-retained FPDs made of two different types of framework material (11 of high-strength pressed ceramic and 12 of fiber-reinforced composite) have been examined in a clinical study. RESULTS: One inlay-retained FPD made of pressed ceramic had to be replaced because of a fracture. Because the materials have only been on the market for a short time, long-term results are not yet available. CONCLUSION: This type of restoration provides excellent esthetics and reduced invasiveness compared with complete crown-retained FPDs, although indications are limited by the special mechanical properties of the material.

Acid Etching, Dental↗
PubMed1999

Crack formation of all-ceramic crowns dependent on different core build-up and luting materials.

OBJECTIVES: The aim of this in vitro study was to evaluate various core build-up and luting materials regarding their effect on crack formation of all-ceramic crowns. METHODS: Fifty-six freshly extracted sound human third molars were prepared according to a standardized procedure obtaining a circular shoulder of 1.5 mm with all margins located in dentin. Sixty percent of the dentin volume were removed and restored with totally bonded build-up composite resins or resin-modified glass ionomer cements (RMGIC) or compomers. Cast IPS-Empress caps were manufactured and luted with the different materials. For each material group, the volumes of the core build-ups and of the luting cements were determined. The caps were examined for cracks after 1, 3, 6, 9 and 12 months storage in 0.9% saline solution at 37 degrees C. RESULTS: The tested groups revealed no major differences in the percentage of the core build-ups and in the volume of the luting cements. After 12 months only the group with composite resin build-up and luting showed no crack formation. RMGIC/compomer build-up or RMGIC/compomer luting always resulted in cracking of the caps. CONCLUSIONS: Within the limits of this study it can be concluded that the hygroscopic expansion of RMGIC/compomer materials led to failure of all-ceramic crowns, when the materials are used for both core build-up or adhesive bonding.

Acrylates↗
PubMed1997

Marginal fit consistency of copy-milled all-ceramic crowns during fabrication by light and scanning electron microscopic analysis in vitro.

The aim of this study was to evaluate the marginal fit of copy-milled Celay In-Ceram crowns after different fabrication steps and to compare light-microscopic with scanning-electron-microscopic data. A master steel die of an upper middle incisor with a shoulder preparation and a rounded inner line angle was used. Impressions were taken to produce 10 working stone dies. One crown per working die was manufactured. The evaluation of the external marginal gap was performed on the master steel die by using a light microscope and a computerized video image analysis system after copy milling (A), glass infiltration (B), and veneering (C). Approximately 3900 readings were taken. In a final series the veneered crowns were measured by using a scanning electron microscope (Cs), yielding approximately 1000 readings. The results obtained were: A mean, 25.1 microm; s.d., 5.1 microm; range, 2.5-76.8 microm: B mean, 20.6 microm; s.d., 2.3 microm; range, 2.5-76.1 microm: C mean, 18.3 microm; s.d., 4.1 microm; range, 2.5-87.2 microm: Cs mean, 23.0 microm; s.d., 7.6 microm; range, 0.0-94.5 microm. The results were statistically evaluated using the t-test. The differences found between the series did not show practical relevance. Therefore, it is concluded that the manufacturing steps after copy milling have no obvious influence on the external marginal gap width. Scanning electron microscopic data seem to confirm the light-microscopic results. Hence, we expect that the Celay In-Ceram method yields a clinically acceptable marginal fit.

Aluminum Oxide↗