Fracture Resistance of Aged Full-Coverage All-Ceramic Zirconia and Metal-Ceramic Restorations of Implant-Supported Fixed Partial Dentures

BACKGROUND: Metal-ceramics restorations were considered a preferable option for fabrication fixed partial dentures (FPDs) that have an acceptable durability, but they are not able to provide the same beauty as the entire ceramic material. Full-contour zirconia, such as Zolid, does not have problems with chipping of layered zirconia, along with translucency and staining capabilities. AIM: This study aimed to assess the fatigue fracture strength of three-unit implant-supported full-contour zirconia and metal-ceramics posterior FPDs. MATERIALS AND METHODS: In this in vitro study, 24 posterior three-unit implant-supported FPDs were fabricated of full-contour zirconia and metal-ceramics and were cemented on implant abutments. To simulate the oral environment, FPDs were subjected to 10,000 thermal cycles between 5 and 55°C for 30 s and were then transferred to a chewing simulator (100,000 cycles, 50 N, 0.5 Hz). Afterward, fatigue fracture strength was measured using a universal testing machine. Data were analyzed using an independent sample t-test. RESULTS: The obtained results showed that the mean and standard deviation of fatigue fracture strength was higher for the metal-ceramics group (2567.8 ± 689.7 N) compared to those for the full-coverage zirconia group (2108.6 ± 455.2 N). However, the difference was not statistically significant (p ˃ 0.05). CONCLUSIONS: Fracture resistance due to fatigue in the metal-ceramics group was not significantly different from full-coverage zirconia group. Full-coverage zirconia seems promising as a metal-ceramics material for the fabrication of posterior three-unit FPDs.

Efficacy of Application of Platelet-Rich Fibrin for Improvement of Implant Stability: A Clinical Trial

Use of platelet concentrates to increase implant stability, due to their regenerative potential, has recently attracted the attention of researchers. This study aimed to assess the effect of platelet-rich fibrin (PRF) on dental implant stability. This clinical trial evaluated 10 patients who received 50 dental implants. Each patient received at least two implants. Half of the implants were placed in the sockets along with PRF while the remaining half were inserted conventionally without PRF. Implant stability was measured by resonance frequency analysis on the day of surgery (T1), at one week (T2), and at one month (T3). At the end of the first week (T2), the mean implant stability quotient (ISQ) was 59.85 ± 5.32 in the PRF group and 55.99 ± 3.39 in the non-PRF group. Compared to baseline, the ISQ increased in the PRF group by 0.12 ± 0.47 (P = 1.000) and decreased in the non-PRF group by 2.42 ± 0.36 (P < 0.001). At one month postoperatively, ISQ significantly increased by 6.89 ± 0.96 in the PRF group and by 4.82 ± 0.92 in the non-PRF group compared to baseline (P < 0.001). Application of PRF in the implant osteotomy site can prevent or minimize primary reductions in implant stability and seems to enhance the process of osseointegration.

Effect of Implant-Abutment Connection Type on Stress Distribution in Peri-Implant Bone and Abutment Micromovement: A Three-Dimensional Finite Element Analysis

This study assessed the effect of implant-abutment connection type on stress distribution in peri-implant bone and abutment micromovement using finite-element analysis (FEA). Dimensions of three implant-abutment designs were measured by a three-dimensional scanner and transferred to SOLIDWORKS. An elemental model was designed using ABAQUS. Each implant was placed in bone at the crestal level. A 100-N load was applied at a 45° angle relative to the longitudinal axis of the implant in the buccolingual direction from the palatal toward the buccal and coronal parts of the abutment. Shear stress, von Mises stress, and micromovement of the abutment relative to the fixture were analyzed. Data were reported qualitatively and quantitatively using ABAQUS. The von Mises stress in all three samples decreased from the crest toward the apical area and was distributed homogenously. Maximum stress concentration was at the most coronal part of the implant body in the midbuccal area. In cancellous and cortical bone, stress decreased from the crest toward the palate and was at its maximum at the midbuccal point in the bone crest. Stress in cortical bone was more homogenous and in cancellous bone was higher. Shear stress was higher in the buccal than in the palatal area, and at its maximum shear stress and equal in the mesiobuccal and distobuccal areas. Micromovement was 4.25 μm in an Astra implant, 5.42 μm in a Intra-Lock implant, and 6.63 μm in an SPI implant. The distribution of von Mises and shear stress was the same in bone around the three implant connection types; however, abutment micomovement differed.

Comparison of interdental papilla around single implants in the anterior maxilla between two implant systems: A cohort study

Background. In successful replacement of a tooth with a dental implant, soft tissue esthetic is as important as stability and function of the implant. Quality and quantity of the peri-implant mucosa can influence esthetic outcomes. This study assessed implant esthetic success of two different implant systems. In this regard the interdental papilla was evaluated and the relation-ship between implant type and crestal bone loss adjacent to implant was assessed.

Methods. Eighteen patients (11 males, 7 females) with a total of 18 implants participated in this historical cohort study. Patients were divided into two groups based on the type of implants: Implantium group and SPI group; 36 interproximal papillae were evaluated photographically, using Jemt’s papillary presence index (PPI). Radiographic analysis was carried out to find out the relation between bone loss and type of implant. Analysis of data was performed with SPSS 18, using Fisher's exact test, independent t-test, Spearman's correlation coefficient and ANOVA.

Results. Comparison of photographs did not show a statistically significant difference in PPI between the two groups (P=0.94). Radiographic evaluation of crestal bone loss adjacent to implant shoulder did not reveal significant differences between the two groups (P=0.30).

Conclusion. Implant therapy in the anterior maxilla, using Implantium or SPI system, did not result in significant differences in esthetics. In this study, there was an inverse relationship between the distance of contact point to bone crest and papilla index (P=0.002 in the SPI group) (P=0.02 in the Implantium group).

Effect of Resin Cement Color on the Final Color of Lithium Disilicate All-Ceramic Restorations

OBJECTIVES

Obtaining an adequate ceramic thickness to mask the substructure color is not always feasible, and appropriate use of a cement may be the only solution. This study aimed to evaluate the effect of the color of Variolink II resin cement on the final color of lithium disilicate glass ceramic restorations.

MATERIALS AND METHODS

In this in-vitro study, 90 discs of IPS e.max Press ceramic were evaluated. The ceramic discs were cemented to composite and amalgam blocks. The effect of the cement color and substructure on the final color of ceramic was analyzed by calculating the color change (ΔE) value using a spectrophotometer. Data were analyzed via three-way analysis of variance (ANOVA) and Tukey's test.

RESULTS

The cement color had a statistically significant effect on the final color of ceramic (P≤0.001). The white, yellow, and translucent cements caused the highest color change (ΔE=4.558, 3.308, and 2.649, respectively). The effect of composite substructure and the yellow cement on the final color was less prominent compared to other combinations of cement and substructure (ΔE=2.043). The white cement over amalgam substructure showed the greatest effect on the final color (ΔE=4.890). The ΔE in HO group was less than that of other combinations (P<0.05), and the greatest ΔE was reported in MO group with the white cement (ΔE=6.255).

CONCLUSIONS

The final color of the restoration is influenced by the cement color. Therefore, when IPS e.max Press is used over a metal core, it is recommended to use a cement with an HO ceramic.

Comparison of in vitro properties of periodontal ligament stem cells derived from permanent and deciduous teeth

Background. Stem cells have contributed to the development of tissue-engineered-based regenerative periodontal therapies. In order to find the best stem cell sources for such therapies, the biologic properties of stem cells isolated from periodontal ligaments (PDL) of deciduous (DePDLSC) and permanent (PePDLSC) teeth were comparatively evaluated. Methods. PDL stem cells were isolated from six sound fully erupted premolars and six deciduous canines of healthy subjects. In vitro biologic characteristics such as colony formation, viability, stem cell marker identification and osteogenic differentiation (using alkaline phosphatase analysis and Alizarin red staining) were comparatively assessed using one-way ANOVA and post hoc Tukey tests using SPSS 13.0. Results. Stem cell populations isolated from both groups were CD105+ and CD90+ and CD45‒. No statistically significant differences were found in stem cell markers, colony formation and viability. Both groups were capable of osteogenic differentiation. However, alkaline phosphatase activity test showed a statistically significant difference, with PePDLSC exhibiting higher alkaline phosphatase activity (P=0.000). No statistically significant difference was seen in quantitative alizarine red staining (P=0.559). Conclusion. Mesenchymal stem cells of PDL could successfully be isolated from permanent and deciduous teeth. A minor difference was observed in the osteogenic properties of the two cell types, which might affect their future clinical applications.

Immediate vs. delayed endosseous integration of maxi implants: a torque removal animal study

Background. Delayed loading is one of the concerns in implant patients. Immediate loading can solve the problem and make patients more satisfied. The present study aimed to compare the removal torque of maxi implants under different loading (immediate and delayed) patterns. Methods. This split-mouth experimental study included 2 dogs. Impressions were made and then all the premolars were extracted under general anesthesia. After a three-month healing period, 3 implants were inserted in each quadrant (a total of 12 implants). Anterior and posterior implants (the case group) were splinted by an acrylic temporary bridge in order to make the middle implants (the control group) off the occlusion. The dogs were sacrificed after 6 weeks and bone blocks were submitted for removal torque test. Data were analyzed with ANOVA (P<0.05). Results. Mean torque values for the cases and control groups were 46.82±25.58 and 59.88±15.19, respectively (P=0.582; not significant). Conclusion. It may be concluded that immediate loading does not reduce the reverse torque values of maxi implants. This supports the advantages of immediate loading for maxi implants.

Fatigue Fracture Strength of Implant-Supported Full Contour Zirconia and Metal Ceramic Fixed Partial Dentures

OBJECTIVES

Zirconia restorations have been suggested as a more durable and more appealing alternative to metal restorations. However, their mechanical properties may be negatively affected by fatigue due to superficial stresses or low temperature degradation. This study aimed to assess the fatigue fracture strength of three-unit implant-supported full contour zirconia and pre-sintered cobalt-chromium (Co-Cr) alloy posterior fixed partial dentures (FPDs).

MATERIALS AND METHODS

In this in-vitro experimental study, 28 posterior three-unit implant-supported FPDs were fabricated of full contour zirconia and pre-sintered Co-Cr alloy, and were cemented on implant abutments. To simulate the oral environment, FPDs were subjected to 10,000 thermal cycles between 5-55°C for 30 seconds, and were then transferred to a chewing simulator (100,000 cycles, 50 N, 0.5 Hz). Afterwards, fatigue fracture strength was measured using a universal testing machine. Data were analyzed by Mann-Whitney U test.

RESULTS

The mean and standard deviation of fracture strength were 2108.6±440.1 N in full contour zirconia, and 3499.9±1106.5 N in pre-sintered Co-Cr alloy. According to Mann-Whitney U test, the difference in this respect was statistically significant between the two groups (P=0.007).

CONCLUSIONS

Since the fracture strength values obtained in the two groups were significantly higher than the maximum mean masticatory load in the oral environment, both materials can be used for fabrication of posterior three-unit FPDs, depending on the esthetic demands of patients.

Accuracy of shade matching performed by colour blind and normal dental students using 3D Master and Vita Lumin shade guides

The purpose of this study was to investigate whether 3D Master or VitaLumin shade guides could improve colour selection in individuals with normal and defective colour vision. First, colour perception of 260 dental students was evaluated. Afterwards, 9 colour blind and 9 matched normal subjects tried to detect colours of 10 randomly selected tabs from each kit and the correct/false answers were counted. Of the colour-defective subjects, 47.8% and 33.3% correctly detected the shade using 3D Master and VitaLumin, respectively. These statistics were 62.2% and 42.2% in normal subjects. In normal participants, but not in colour blind ones, 3D Master significantly improved shade matching accuracy compared to VitaLumin.

Comparative Stress Distribution of Implant-Retained Mandibular Ball-Supported and Bar-Supported Overlay Dentures: A Finite Element Analysis

Implant-retained mandibular ball-supported and bar-supported overlay dentures are the two most common treatment options for the edentulous mandible. The superior option in terms of strain distribution should be determined. The three-dimensional model of mandible (based on computerized tomography scan) and its overlying implant-retained bar-supported and ball-supported overlay dentures were simulated using SolidWorks, NURBS, and ANSYS Workbench. Loads A (60 N) and B (60 N) were exerted, respectively, in protrusive and laterotrusive motions, on second molar mesial, first molar mesial, and first premolar. The strain distribution patterns were assessed on (1) implant tissue, (2) first implant-bone, and (3) second implant-bone interfaces. Protrusive: Strain was mostly detected in the apical of the fixtures and least in the cervical when bar design was used. On the nonworking side, however, strain was higher in the cervical and lower in the apical compared with the working side implant. Laterotrusive: The strain values were closely similar in the two designs. It seems that both designs are acceptable in terms of stress distribution, although a superior pattern is associated with the application of bar design in protrusive motion.

Comparison of stresses induced by fiber post, parapost and casting post in root canals by photoelasticity method

INTRODUCTION

Many studies have been performed to evaluate the stress distribution around endodontic posts; those which compared posts composed of different materials are rare. The aim of this study was to compare stresses induced in dentin by three structurally different posts using photoelasticity method.

MATERIALS AND METHODS

Nine blocks of PSM-5 Photoelastic material with 45×45×10 mm dimension were prepared. In each block, a canal 9 mm in length and 0.8 mm in width was drilled. Blocks were divided into 3 groups of three each. In the first group, the canals were prepared for insertion of Fiber Post with 1.25 mm width. In the second group, the canals were prepared for insertion of ParaPost with 1.25 mm width and the canals in the third group were prepared for casting post similar to the above samples. Casting Post pattern was made by Duralay resin and casted by Ni-Cr alloy. All posts were cemented in canals with Panavia cement. The stresses were evaluated in the polariscope under three different conditions: 1) without load, 2) with 135 N vertical load, and 3) with 90 N oblique load (26° inclination to post long axis). The fringe orders in the cervical, middle and apical regions of the posts were evaluated and compared with each other.

RESULTS

Application of the vertical load induced a high stress concentration (FO=4) in the apical region of the ParaPost, while lower stress was observed in the middle (FO=2) and cervical region (FO=2+). Fiber Post and Casting Post showed even stress distribution (FO=2+). High stress concentration was detected with the application of oblique force in the cervical region of ParaPost (FO=5) and Casting Post (FO=3+). Fiber Posts fractured before reaching 90-N loading force.

CONCLUSION

The stress distribution around Fiber Post and Casting Post were constant in comparison with ParaPost. Fiber Post with 1.25 mm width was not recommended in situations with high oblique stresses.

Multiple in vitro analyses of fracture resistance in maxillary central incisors restored with fiber posts

INTRODUCTION

The resistance to fracture of endodontically treated teeth restored with esthetic post systems has not been extensively researched. This in vitro study compared the fracture patterns of endodontically treated teeth with esthetic post systems with different analysis methods.

MATERIALS AND METHODS

A total of 26 recently extracted human maxillary central incisors were decoronated and then endodontically treated. Teeth were restored with quartz fiber posts. All posts were cemented with Panavia dual curing adhesive resin cement and subsequently restored with composite cores. Three methods were used to test fracture resistance. Each specimen was embedded in acrylic resin and then secured in a universal load-testing machine. A compressive load was applied at 135º degree angle at a crosshead speed of 1 mm/min to the long axis of the tooth until fracture occurred. The two other methods, finite element analysis (FEA) and photo elastic study used the same angulation and 90 N force to simulate the first method. The data were then compared.

RESULTS

Clinical results indicated that fracture was most likely to occur between core and dentin, and then in the cervical 1/3 of the root. Photo elastic study demonstrated similar results; the highest stresses occurred at the junction of dentin and core contralateral to the side where force was applied. FEA also confirmed these results; however it also showed that the highest stresses arise at the dentin/core junction contralateral to the force point.

CONCLUSION

All three techniques reiterate that the risk of fracture is greatest at the cervical dentin/core junction.