Fracture resistance and marginal gap formation of post-core restorations: influence of different fiber-reinforced composites

Clinical Oral Investigations - The aim was to explore the fracture behavior and marginal gap within the root canal of endodontically treated (ET) premolars restored with different fiber-reinforced...     

Fracture resistance of re-attached coronal fragments – influence of different adhesive materials and bevel preparation

Abstract – The purpose of this study was to investigate the fracture resistance of re‐attached coronal fragments of teeth using different materials and tooth preparations. Seventy‐two recently extracted bovine incisors were selected. Eight incisors were maintained without any preparation as a control group. The incisal third of the other teeth was sectioned using a diamond saw. In one group (n = 32), a 2‐mm bevel was prepared, whereas in the second group no preparation was made (n = 32). The specimens (beveled and non‐beveled) were divided in four groups (n = 8) and re‐attached with the following materials: a dual‐cured resin cement RelyX ARC (RX); a chemically cured composite Bisfil 2B (B2); a light‐cured composite Z250 (Z2); and a one‐bottle adhesive Single Bond (SB). The bevel region was restored with adhesive and composite. All materials were used according to manufacturer's directions. A light‐curing unit was used to polymerize the materials. Specimens were stored in saline solution for 72 h. De‐bonding procedures were performed in a testing machine with cross‐head speed of 0.6 mm min^?1. The load was applied in the incisal third. The resistance to fracture for control group was 70 (7) kg. The fracture resistance for non‐beveled and beveled specimens were: SB, 3.3 (2.4) and 17.0 (4.1); RX, 11.5 (3.0) and 16.3 (3.1); Z2, 14.4 (4.2) and 20.5 (1.7); and B2, 19.5 (3.5) and 32.5 (7.4) kg. Analysis of variance (anova ) and Fisher's protected least significant difference (PLSD) test disclosed significant influence for materials and cavity designs (P = 0.001). The highest failure loads were obtained with the B2 group and then with the Z2 with either bevel or non‐bevel. RX produced lower failure loads than the restorative composites. The lowest failure load was obtained with SB in the non‐beveled group. No technique studied was able to attain the fracture resistance of the control group and both materials and tooth preparation influenced the fracture resistance.     

Marginal gap formation of composites in dentine: effect of water storage

This study investigated the effects of water storage on the marginal adaptation of two composite resins (Spectrum TPH and Ariston AT), two polyacid-modified composite resins (Dyract AP and F2000) and a new PRG composite (Reactmer) to dentine over time. Two cylindrical dentine cavities (1.5 mm diameter and 1.5 mm deep) were prepared on the horizontally sectioned surfaces of freshly extracted teeth. In each tooth, one cavity was restored using composites with their respective bonding system and the other without the bonding system. The sample size for each material with/without bonding system was 6. The composites were placed in one increment, bulk-polymerized, immediately finished/polished with the Sof-lex discs system and fine polished on 30 microm silicon carbide/9 microm aluminium oxide lapping film discs in a microgrinding system. The specimens were then stored in distilled water at 37 degrees C and the maximum marginal gap width between the material and the dentine wall was determined at 24 h, 1 week, 2 weeks, 3 weeks and 4 weeks using a measurescope at x500 magnification. Results were subjected to statistical analysis using monva, anova/Scheffe's post hoc test and independent samples of t-test at significance level 0.05. At all time intervals, no significant difference in marginal gap formation was observed between materials. Where bonding systems were not used, a decrease in gap widths over time was observed with most materials but only Dyract AP exhibited a significant decrease. The latter was observed after 2 weeks storage in water. The use of bonding systems reduced dentine marginal gaps significantly and is therefore mandatory for all composites evaluated. Marginal gaps arising from polymerization contraction of conventional, polyacid-modified and PRG composites cannot be fully compensated by hydroscopic expansion. Clinical relevance Bonding systems are mandatory for all composites when bonding to dentin. In the event of a bond failure at placement, hygroscopic expansion of composites can reduce marginal gaps but not completely.     

The influence of C-factor, flexural modulus and viscous flow on gap formation in resin composite restorations

This study analyzed the influence of C-factor, flexural modulus and viscous flow on gap formation in resin composite restorations. Two resin composites, a mini-filled hybrid (P 60) and a nanofilled (Supreme), were used. The flexural modulus was obtained from bar-shaped specimens submitted to three-point bending. Viscous flow was obtained from the difference between the initial and final diameter of resin composite disks submitted to a load of 10 N for 120 seconds. Gap analysis was conducted in three types of cylindrical cavities (C-factor of 1.8, 2.6 and 3.4) that were prepared on the occlusal surfaces of human molars. The gap width at the dentin-resin composite interface was measured using a 3D scanning system (Talyscan 150). The data were analyzed by ANOVA and Student-Newman-Keuls' test, t-test and linear regression analysis (alpha = 0.05). The cavities with C-factor 3.4 presented the highest Gap formation (p < 0.0001). The lowest Gap formation was found in cavities restored with Supreme resin composite (p < 0.0001). P 60 presented significantly higher flexural modulus and lower viscous flow than Supreme (p < 0.0001). Regression analyses detected a significant influence of flexural modulus and viscous flow on gap formation (p < 0.05).     

Influence of preparation features on retention and resistance. Part I: MOD onlays

Four variations of an MOD onlay preparation were studied for retention and resistance. Boxes were more effective than an isthmus in increasing retention value. The combination of boxes and isthmus showed the highest retention. The combination of boxes and isthmus also exhibited the highest resistance. There was no difference in resistance between boxes and the isthmus.     

Fracture resistance and marginal discrepancy of porcelain laminate veneers influenced by preparation design and restorative material in vitro

ObjectivesThe purpose of this investigation is to evaluate marginal discrepancy and fracture resistance of two veneering materials using two preparation designs.MethodsTwo veneer preparation designs (full and traditional) were restored with leucite-reinforced ceramic (ProCAD, Ivoclar Vivadent, Amherst, NY) milled by CAD/CAM (Cerec 3D milling system, Serona Dental Systems), and conventional sintered feldspathic porcelain (Noritake Super Porcelain EX3, Noritake Dental Supply Co). Forty-eight specimens were analysed with a sample size of n = 12 per group. The thickness of each veneer was measured on four specific surfaces. Marginal discrepancy was evaluated with a replica technique and cross-sectional view using a digital microscope. The fracture resistance of veneers cemented on standardised composite resin dies was evaluated using a universal testing machine. Results were analysed with ANOVA, Tukey–Kramer post hoc testing, and linear regression.ResultsThe results of this investigation revealed no correlation between the thickness and marginal discrepancy of the veneers. The full preparation design with ProCAD and the traditional preparation design with feldspathic porcelain manifested smaller gap. Fracture resistance was decreased for the full preparation design with feldspathic porcelain.ConclusionsIn terms of marginal discrepancy and fracture resistance, the most favourable combination was a traditional veneer preparation design with conventional sintered feldspathic porcelain. For the full veneer preparation, a stronger ceramic material such as ProCAD is suggested.     

Influence of restorative material and proximal cavity design on the fracture resistance of MOD inlay restoration

Objective

This study aimed to evaluate the effects of the restorative material and cavity design on the facture resistance of inlay restorations under a compressive load using acoustic emission (AE) measurement.

Materials and methods

Two restorative materials, a composite resin (MZ100, 3M ESPE) and a ceramic (IPS Empress CAD, Ivoclar Vivadent), and two cavity designs, non-proximal box and proximal box, were studied. Thirty-two extracted human third molars were selected and divided into 4 groups. The restorative materials and cavity designs used for the four groups were: (1) composite and non-proximal box; (2) ceramic and non-proximal box; (3) composite and proximal box; (4) ceramic and proximal box. The restored molars were loaded in a MTS machine via a loading head of diameter 10 mm. The rate of loading was 0.1 mm/min. During loading, an AE system was used to monitor the debonding and fracture of the specimens. The load corresponding to the first AE event, the final maximum load sustained, as well as the total number of AE events recorded were used to evaluate the fracture resistance of the restored teeth.

Results

For the initial fracture load, Group 2 (236.15 N) < Group 1 (428.14 N) < Group 4 (441.24 N) < Group 3 (540.06 N). The same trend was found for the final load, i.e., Group 2 (1594.68 N) < Group 1 (2003.82 N) < Group 4 (2004.89 N) < Group 3 (2057.53 N). For the total number of AE events, Group 4 (2135) > Group 2 (1685) > Group 3 (239) > Group 1 (221). The differences from pairwise comparisons in the initial fracture load and final load were mostly insignificant statistically (p > 0.05), the only exception being that between Groups 2 and 3 in the initial fracture load (p = 0.039). For the total number of AE events, statistically significant differences (p < 0.05) were found between all group pairs that involved different materials, with the composite groups giving much fewer AE events than the ceramic groups. Conversely, no statistically significant difference in the AE results was found between groups with the same material, irrespective of the cavity design.

Significance

For teeth restored with MOD inlays, the use of composite resin as the restorative material may provide higher fracture resistance than using ceramic. Using a proximal box design for the cavity may further improve the fracture resistance of the inlay restoration, although the improvement was not statistically significant under axial compression.     

Fracture resistance of single-tooth implant-supported all-ceramic restorations: an in vitro study

STATEMENT OF PROBLEM: High-strength ceramic materials can be used to fabricate esthetic and stable implant-supported single-tooth restorations. No study was identified that compared the fracture resistance of individual components of single-tooth implant-supported all-ceramic restorative systems after artificial aging. PURPOSE: The purpose of this in vitro study was to evaluate the fracture resistance of single-tooth implant-supported all-ceramic restorations consisting of alumina all-ceramic restorations on different implant abutments and to identify the weakest component of the restorative system. MATERIAL AND METHODS: Forty-eight standardized maxillary central incisor alumina crowns (Procera) were fabricated for each of the 3 test groups (n = 16) (Control group Ti, titanium abutments; Group Al, alumina abutments; Group Zr, zirconia abutments) for the Replace implant system. The crowns were adhesively luted using a resin luting agent (Panavia 21) and artificially aged through dynamic loading and thermal cycling. Afterwards, all specimens were tested for fracture resistance using compressive load on the palatal surfaces of the crowns. Kruskal-Wallis analysis of variance and post hoc Wilcoxon rank sum tests were performed to test for differences in fracture resistance values (alpha = .05). RESULTS: All test specimens survived the artificial aging process using simulated oral conditions. No screw loosening was recorded. The median fracture resistance was 1454 N, 422.5 N, and 443.6 N for groups Ti, Al, and Zr, respectively. Significant differences were found for the fracture resistance comparisons of group Ti with groups Al and Zr (Kruskal-Wallis test, P < .001). The test results for the comparison of groups Al and Zr were not significant. CONCLUSION: All 3 implant-supported restorations have the potential to withstand physiologic occlusal forces applied in the anterior region.     

Microleakage and gap formation of resin composite restorations polymerized with different techniques

PURPOSE: To evaluate the effect of different polymerization techniques on microleakage and gap formation of resin-based composite restorations. One correlation test was also carried out between these methodologies. METHODS: 180 vertical slot cavities were prepared in bovine teeth and filled with Z250/Single Bond system, for the following six groups (n=30): Soft-start I - 10 seconds at 75 mW/cm2 + 30 seconds at 560 mW/cm2; Soft-start II - 10 seconds at 190 mW/cm2 + 30 seconds at 560 mW/cm2; Pulse delay - 3 seconds at 300 mW/cm2 + 5 minutes waiting + 30 seconds at 560 mW/cm2; Plasma arc - 3 seconds at 1,500 mW/cm2; High intensity - 40 seconds at 810 mW/cm2; Conventional (control) - 40 seconds at 560 mW/cm2. After polishing, epoxy replicas were prepared for electron microscopy analysis (n=10), at x500 magnification. The samples were thermocycled, new epoxy replicas were prepared, and the teeth were immersed in 2% methylene blue dye solution for 4 hours. Marginal gaps were evaluated again and the microleakage was assessed. RESULTS: No statistical difference among polymerization techniques was observed for microleakage (Kruskal-Wallis test). For gap formation there was no statistical difference among polymerization techniques either before or after thermocycling (Tukey test). Conversely, thermocycling significantly increased the gap formation for all groups. No correlation (Spearman correlation test) was observed for the results of microleakage and gap formation.     

Effect of liners on cusp deflection and gap formation in composite restorations

This study measured deformation of cusps and gap formation associated with MOD resin composite restorations in maxillary premolars with and without the use of low elastic modulus liners. Low elastic modulus liners may reduce the deformation by absorbing polymerization shrinkage stress. Forty maxillary premolars were mounted in stone and slot MOD cavities were prepared. Teeth were randomized into four groups. In Group A, cavities were etched, Single Bond was applied and the cavities were restored with Z-100 composite. In Group B, the same was done except that a layer of flowable composite (Revolution) was place and cured after the bonding agent. In Group C, the same steps were followed as Group A but a layer of glass ionomer (Vitrebond) was placed and cured before the bonding agent. In Group D, a thin layer of composite was placed (after the bonding agent) as a base and cured and the cavities were filled. The distance between indexed cusp tips was measured before the restorations were finished and five minutes and 24 hours after the restorations were completed. The samples were then sectioned mesiodistally and epoxy resin replicas were made and prepared for SEM evaluation of gap formation. The mean contraction of the cusps in microm at 5 minutes and 24 hours, respectively, for each group was A) 47 and 30, B) 35 and 21, C) 23 and 8 and D) 40 and 28. Groups A and D resulted in the highest deformation, B was intermediate and C was the lowest. There was no statistically significant difference in gap formation between the groups.     

Modified Class II open sandwich restorations: evaluation of interfacial adaptation and influence of different restorative techniques

The sandwich technique with resin-modified glass ionomer cement (RMGIC) has been proposed to relieve the contraction stresses of direct resin composite (RC) restorations. The aim of this study was to evaluate the interfacial adaptation to enamel and dentin of modified Class II open RMGIC/RC sandwich restorations and the influence of different light curing techniques and matrix bands. Forty box-shaped Class II fillings were placed in vivo in premolars scheduled for extraction after one month. In groups I and II, a metal matrix was used; RC was inserted with horizontal (group I) and diagonal (group II) increments and cured with indirect/direct light. Group III was performed as group II, but a transparent matrix was used. Group IV was as group II, but with a separating liner between RMGIC and RC. Group V was a closed sandwich restoration. Interfacial quality was studied using SEM replica technique. Gap-free interfacial adaptation to enamel was observed for RMGIC in 70%, for RC in 70% and to dentin for RMGIC in 81%, for RC in 56%. No significant differences were seen between the experimental groups. At the cervical margins, RMGIC showed significantly better adaptation to enamel than RC, 74% and 42%, respectively. In conclusion, the investigated restorations showed a high percentage of gap-free interfacial adaptation in vivo. Interfacial adaptation to dentin and to cervical enamel was significantly better for RMGIC than for RC.     

Fracture resistance of different partial-coverage ceramic molar restorations: An in vitro investigation

BACKGROUND: The authors conducted a study to evaluate the influence of preparation design on reliability and fracture resistance of press-ceramic posterior partial-coverage restorations (PCRs) under fatigue. They compared the results for PCRs fabricated of a new press ceramic (IPS e.max Press-VP 1989/4, Ivoclar-Vivadent, Schaan, Liechtenstein) with results for ceramic inlays and unprepared molars. METHODS: The authors randomly divided 96 human upper molars into six equal groups. Control group NP specimens remained unprepared. Control group IN specimens received a mesio-occlusal-distal (MOD) inlay preparation. The test groups received PCR preparation designs based on group IN's inlay design, with additional cuspal reduction that increased from group to group. The authors fabricated 16 ceramic inlays and 64 PCRs of IPS e.max Press and luted them adhesively. All specimens underwent masticatory fatigue loading (1.2 million cycles, 1.6 hertz, 98 newtons), 5,300 thermal cycles and observation for fracture patterns. Afterward, the authors loaded all surviving specimens until fracture. RESULTS: No fractures occurred during the exposure to the masticatory simulation. After undergoing loading in a universal testing machine, the groups showed no significant differences in fracture strength values (P = .6026). Thus, the different preparation designs of the PCRs demonstrated no significant influence on the restorations' fracture resistance. The median failure loads ranged from 1,567 to 1,960 newtons. CONCLUSION: All-ceramic PCRs for molars made of IPS e.max Press were shown to be fracture-resistant, results comparable with those of natural unprepared teeth. CLINICAL IMPLICATIONS: When a posterior ceramic PCR is indicated, the clinician should perform a defect-oriented preparation that preserves tooth structure. Further clinical investigations are recommended to verify the authors' in vitro results.     

Influence of the bulk fill restorative technique on microleakage and microtensile of class II restorations

Background & AimThe aim of this study is to evaluate microleakage and bond strength test of the bulk fill restorative technique.Materials and methodsÆLITE LS Posterior and SureFil SDR flow were used as composite restoration, and Clearfil S³ (Self Etch system) Bond and Prime&Bond NT (Total Etch system) were used as bonding agents. Standardized Class II cavities were made on sixty extracted premolar teeth and they were randomly divided into four groups. Thermo-cycling and mechanical loading was applied to all samples. The samples were stored in the %2 basic fuchsine solutions and the microleakage was evaluated.ResultsWhen total etching system groups were evaluated, the cervical microleakage values were higher than occlusal microleakage values on both composites (P < 0.05), but there were no differences between the self-etch groups. Microtensile test was also applied to the samples. When the MPa values of all groups were compared, there was a very significant difference statistically (P < 0.001).ConclusionsThe results support the conclusion that the SureFil SDR flow exhibited the best performance in occlusal margins of Prime&Bond NT-SureFil SDR groups.     

Fracture resistance of thermal cycled and endodontically treated premolars with adhesive restorations

STATEMENT OF PROBLEM: Cavity preparations have routinely been associated with decreased fracture strength of restored teeth. PURPOSE: The purpose of this study was to evaluate the influence of endodontic treatment and thermal cycling on the fracture resistance of teeth restored with ceramic or composite resin inlay restorations. MATERIAL AND METHODS: One hundred sound, maxillary premolars were selected. Twenty intact teeth served as a control group. Eighty teeth were prepared with MOD cavity preparations; half of them were also endodontically treated. Inlay restorations were prepared with composite resin (Filtek Z250) or feldspathic ceramic (Vitadur Alpha). Half of the specimens for each group were submitted to thermal cycling (500 cycles, between 5 and 55 degrees C, dwell time of 30 seconds). The specimens were subjected to compressive axial loading using a steel ball. Data were analyzed using 3-way ANOVA and post hoc Tukey's test (alpha=.05). RESULTS: Except for those teeth restored with ceramic without endodontic treatment and thermal cycling, no other group achieved fracture strength similar to sound teeth. Ceramic and composite resin restorations provided similar resistance to fracture. There was a significant interaction between endodontic therapy and thermal cycling (P<.001). In the nonthermal cycled groups, endodontically treated teeth showed significantly lower fracture resistance (P<.001). All experimental groups had similar fracture strength when submitted to thermal cycling. CONCLUSIONS: Both restorative techniques provided similar fracture resistance. Endodontic treatment decreased the fracture resistance of nonthermal cycled specimens, while thermal cycling decreased the fracture resistance of nonendodontically treated specimens.     

Fracture resistance of lower molars with Class 1 composite and amalgam restorations

Groups of lower molars with medium Class 1 cavities were restored with amalgam and hybrid composite resins and subjected to centric and eccentric loads on the occlusal surfaces via steel spheres. Sound teeth and teeth with prepared but unrestored cavities were also studied for comparison. Teeth loaded under ‘eccentric’ conditions via large steel spheres sustained higher fracture loads than did corresponding specimens subject to centric loading. Under the eccentric loading mode hybrid composite materials restored the teeth to the strength level of sound teeth. One of these materials (Occlusin) strengthened the teeth to a significantly greater extent than did amalgam.     

Fracture resistance of teeth with Class 2 silver amalgam, posterior composite, and glass cermet restorations

This article reports the fracture resistance of maxillary premolars in which ideal class 2 mesio-occlusal or disto-occlusal cavities were prepared and restored with silver amalgam, posterior composite, and glass cermet. Sound teeth and teeth with prepared but unrestored cavities were also studied for comparison. Dentin-bonded posterior composite resin produced the best tooth fracture resistance, followed by glass cermet, intact teeth, silver amalgam, and unrestored-prepared teeth, in that order.     

Diagnostically generated anterior tooth preparation for adhesively retained porcelain restorations: rationale and technique

A diagnostically based protocol for anterior tooth preparations for adhesively retained porcelain restorations offers dentists and laboratory technicians new options to approaching these restorations. Rather than designing a preparation and restoration based more on the needs of the products used than on the preservation of the remaining tooth structure, practitioners can enhance the predictability of these restorations by concentrating simultaneously on three distinct zones of the tooth (incisal, middle, and cervical) and four diagnostic categories (periodontal, biomechanical, functional, and dentofacial). The result of following the technique presented in this article is achieving an individualized design that offers a predictable option with minimal risks to the remaining tooth structure.