Assessment of Various Post Systems' Fracture Resistance after Endodontic Treatment

Objectives

The study's objective is to evaluate the fracture resistance of a tooth that has had endodontic treatment and has been rebuilt using various post and core systems.

Materials and Methods

Thirty-six extracted premolar teeth of similar sizes were picked, and at random, they were separated into three groups: group A received stainless-steel posts, group B received zirconia fiber posts, and group C received glass fiber posts. Dual-cured resin cement was used to cement each post. The acrylic resin blocks have samples imbedded in them. Additionally, fracture loads were measured while a compressive force was given to the tooth at a crosshead speed of 1 mm/minute. The one-way analysis of variance F-test and post hoc Tukey's test were then used to analyze the results.

Results

When the mean values and standard deviation were compared, it was found that glass fiber posts had the highest fracture resistance, followed by posts made of zirconia fiber, while stainless-steel posts had the lowest fracture resistance.

Conclusion

When compared to zirconia posts and stainless-steel posts, glass fiber posts had the highest level of fracture resistance.

Formulations of NaOCl-based in liquid, gel form or with surfactants on dentin deproteinization before fiber post cementation

The objective of the study was to evaluate the effects of dentin deproteinization protocols for post space using different formulations containing sodium hypochlorite before fiber post cementation with self-adhesive resinous cement. The groups were divided according to the irrigation protocol (DWC, SHS, SHT and SHG). The residue cleanliness, bond strength, adhesive failure pattern, and tag formation at the adhesive interface between the self-adhesive cement and the dentin were evaluated. For this, analysis in scanning electron microscope, push-out test and confocal laser scanning microscopy were performed. The SHT protocol showed the highest residue cleanliness on the dentin surface of the post space (p<0.05). In addition, SHT protocol showed highest bond strength and tag formation in the cervical and middle thirds (p<0.05). Dentin deproteinization with sodium hypochlorite with surfactant provided the best dentin cleaning of residues, bond strength and tag formation after cementation of the fiber post with self-adhesive cement.

Fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters (in vitro study)

BACKGROUND

Fracture resistance of post-core restoration depends on the design of the post, post diameter, post length, the type of adhesive cement used along with material of the core. Despite the different studies concerning the effect of post space diameter on the fracture resistance of endodontically treated teeth, more information regarding fracture resistance and the effect of different post space systems/materials and diameters is required.

AIM OF THE STUDY

This study aimed to evaluate fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters.

MATERIALS AND METHODS

Twenty freshly extracted maxillary central incisors were collected for this study. They were randomly divided into four groups according to intracanal post and its diameter. Group GN (glass-fiber post of 10-mm length and 1.3-mm diameter with composite core), group GW (glass-fiber post of 10-mm length and 1.75-mm diameter with composite core), group ZN (custom-made zirconia one-piece post-core of 10-mm length and 1.3-mm diameter) and group ZW(custom-made zirconia one-piece post-core of 10-mm length and 1.75-mm diameter). Fracture resistance for all samples was evaluated using the universal testing machine under a static load. The data was collected and statistically analyzed using One-Way ANOVA test. Modes of failure were assessed using stereomicroscope for each group.

RESULTS

The highest mean fracture resistance was recorded in group GW (638.7 ± 285.1 N), followed by group ZW (598.5 ± 127.6 N), then GN group (442.8 ± 65.38 N). The lowest mean fracture resistance was recorded in group ZN (435.3 ± 117.3 N). One-Way ANOVA test revealed that there was no statistically significant difference in fracture resistance values among the groups.

CONCLUSION

Post space diameter had an impact over the fracture resistance of endodontically treated teeth. Modulus of elasticity of post material had a major effect on the fracture resistance and mode of failure along with the restorability of the restored tooth. However, there was no statistically significant difference among the tested groups.

Profiles of gut microbiota associated with clinical outcomes in patients with different stages of SARS-CoV-2 infection

The correlation between SARS-CoV-2 infection and gut microbiota has been a subject of growing interest in recent research endeavors. It is postulated that SARS-CoV-2 might lead to gut dysbiosis by affecting the gut-lung axis and reducing the production of antimicrobial peptides in the gastrointestinal tract. Our comprehensive review of both in vivo and clinical studies has revealed a consistent decline in alpha diversity and increased dissimilarity in beta diversity of gut microbiota in comparison to healthy populations, observed during both the acute and post-infection phases of COVID-19. Furthermore, there is a notable reduction in the number of beneficial butyrate-producing bacteria, alongside an upsurge in opportunistic bacteria. Concomitantly, the functional and metabolic characteristics of gut microbiota are significantly altered. Consequently, COVID-19 patients exhibit a heightened inflammatory state, which has been linked to the severity of the disease in the acute phase and the occurrence of post-acute COVID-19 syndrome (PACS) in the post-infection phase. Notably, certain specific gut microbiota species have emerged as potential candidates for aiding in the diagnosis, prediction of disease severity, or treatment of severe cases of COVID-19. This review also underscores the significance of gut microbiota in the context of post-acute COVID-19 syndrome (PACS) and offers valuable insights into possible biomarkers for diagnosis and therapeutic targets for PACS in the future.

[Investigation and analysis of occupational hazard factors in different industries in Tongliao City]

Objective: To investigate the occupational hazard factors of different industries in Tongliao City, and to provide scientific basis for the prevention and control of occupational disease in Tongliao City. Methods: In July 2021, the detection data of coal dust, silica dust, cement dust, benzene, noise and other occupational hazard factors, as well as the occupational health examination data of workers in various positions of 104 enterprises in different industries in Tongliao City were cllected and anylazed. χ(2) test was used to analyze the results of chest radiography of workers in different age groups. Results: A total of 104 enterprises were investigated, and the median time-weighted average concentration (C(TWA)) of coal dust, silic a dust, cement dust and benzene in contact with test posts were 0.94, 0.30, 0.70 and 0.95 mg/m(3), respectively. The median 8 h equivalent sound level (L(EX, 8 h)) of noise was 74.1 dB (A) . The over standard rates of silica dust, cement dust and noise contact positions were 10.83% (16/240) , 7.14% (2/28) and 0.48% (3/628) , respectively. The differences of chest X-ray examination of coal dust and silica dust workers in different working ages were statistically significant (χ(2)=218.50, 531.80, P<0.001) . The difference of hearing threshold of noise workers with different working age was statistically significant (χ(2)=1290.00, P<0.001) . The rates of leukopenia and neutropenia were 41.90% (44/105) and 20.95% (22/105) in benzene exposed workers. The positive rate of brucella exposure workers was 1.33% (1/75) for tiger red plate agglutination test and 3.23% (3/93) for tube agglutination test. Conclusion: Silica dust, cement dust and noise exceed the standard in some posts and places in the Tongliao City, and some workers are infected with Brucella. In the future, we can focus on monitoring noise-generating posts, strengthen supervision and implement prevention and control measures to reduce the incidence of occupational diseases.

The effects of different root canal irrigation protocols and artificial aging procedures on the bond strength between dentin and hybrid ceramic posts

The purpose of this study is to investigate the effects of different root canal irrigation protocols applied to the dentin and artificial aging procedures on the micro pushout bond strength (mPBS) between dentin and hybrid ceramic posts. Seventy-five single-rooted mandibular premolar teeth were divided into 5 groups (Gr1-5). 50 of the teeth were used for the mPBS tests (n = 10), whereas 25 were used for the smear layer examinations (n = 5). Post space were prepared and irrigated with different irrigation-protocols in each group. (Gr1:[SS], Gr2:[NaOCl] + SS, Gr3:[EDTA] + NaOCl + SS, Gr4:[MA] + NaOCl + SS, Gr5:[Ch] + NaOCl + SS). Post and core pattern were fabricated with pattern resin and a fiber post, after scanning, the posts were milled with Vita Enamic resin ceramic block, and cemented. After 7 days the roots were sliced at thicknesses of 1 mm; half of them were subjected to mPBS test, while the other half were tested after undergoing mechanical cycling for artificial aging. For data analysis, the Shapiro-Wilk test was utilized to test normal distributions, 3-way analysis of variance was used to compare mPBS, and Tukey's HSD test was conducted for multiple comparisons. SEM analysis was performed for examination of failure modes and smear layer removal. Different root canal irrigation protocols affected mPBS significantly. While Gr4 had the highest mPBS, Gr1 had the lowest. Regarding to different zones, the highest mPBS was in coronal zone, and the lowest one was in the apical zone. The aging procedure also led to a statistically-significant decrease in mPBS. Most frequent failure modes were cohesive failure in dentin and mixed failure. Irrigation with 7%MA (Gr4) showed better performance than 17% EDTA (Gr3) in smear layer removal, especially at the apical zone of the tooth. This is critical for the success of root canal treatment and increased the mPBS to a higher extent in all zones of the tooth.

Vertical root fracture resistance and crack formation of root canal-treated teeth restored with different post-luting systems

The aim was to investigate the vertical root fracture (VRF) resistance and crack formation of root canal-treated teeth restored with different post-luting systems. Human maxillary lateral incisors of similar size were decoronated, assigned to five groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligament. After root canal filling, post spaces were prepared to place coated fiber-reinforced composite (FRC) or sandblasted titanium (Ti) posts of the same shape and size. Half of the posts were zinc phosphate cemented (C), while the other half was adhesively luted (A). Untreated teeth served as control. After thermal cycling and staircase loading in a chewing simulator, the crack formation on the root dentin surface was microscopically examined and classified as no defect, craze line, vertical crack, and horizontal crack. Subsequently, the samples were loaded until root fracture. Data were analyzed by one-way ANOVA, Tukey’s test, and Fisher’s exact test. All samples survived the chewing simulation without VRF, but crack formation was significantly different between the groups (P = 0.009). The control showed significantly fewer defects than FRC/C, Ti/C, and Ti/A (P = 0.001, P = 0.008, P = 0.008, respectively). FRC/C showed the highest incidence of vertical cracks. FRC/A had the lowest incidence of defects. There was no significant difference in VRF resistance between the groups (P = 0.265). Adhesively luted FRC posts did not increase VRF resistance but reduced the risk of defects. Most defects were craze lines and vertical root cracks.

Posts in Primary Teeth-Past to Present: A Review of Literature

Early childhood caries is indeed a devastative situation for both patients’ parents and pediatric dentists. The primary goal in treating severe early childhood caries is to restore normal function such as maintenance of mesiodistal and vertical dimension, prevention of alteration of mastication, phonetics (due to premature loss), development of parafunctional habits, and prevention of psychological problems affecting the self-esteem of a child. The restoration of primary dentition with extensive carious lesions is a complex clinical challenge of several dimensions. The severity of this condition in maxillary anterior teeth has prompted the extraction of teeth due to inadequate esthetic treatment options. The only concern with the severely destructed primary incisors is a lack of crown structure, which fails to support and adhere to a composite crown. Clinicians have preferred many restorative modalities for esthetic rehabilitation of badly decayed anterior primary teeth with numerous root canal retentive post and core systems with appropriate techniques to preserve those teeth until they are replaced by permanent teeth. This review highlights the various posts, their indications, principles, ideal properties, and the current concepts on their use in pediatric dentistry.

Exploring the cause of the dual allosteric targeted inhibition attaching to allosteric sites enhancing SHP2 inhibition

SHP2 is a protein tyrosine phosphatase (PTP) that can regulate the tyrosine phosphorylation level. Overexpression of SHP2 will promote the development of cancer diseases, so SHP2 has become one of the popular targets for the treatment of cancer. Studies have reported that both SHP099 and SHP844 are inhibitors of SHP2 and bind to different allosteric sites 1 and 2, respectively. Studies have shown that combining SHP099 with SHP844 will enhance pharmacological pathway inhibition in cells. This study uses molecular dynamic simulations to explore the dual allosteric targeted inhibition mechanism. The result shows that the residues THR108-TRP112 (allosteric site 1) move to LEU236-GLN245 (αB-αC link loop in PTP domain) , the residues of GLN79-GLN87 (allosteric site 2) get close to LEU262-GLN269 (αA-αB link loop in PTP domain) and HIS458-ARG465 (P-loop) come near to ARG501-THR507 (Q-loop) in SHP2-SHP099-SHP844 system, which makes the "inactive conformation" more stable and prevents the substrate from entering the catalytic site. Meanwhile, residue GLU110 (allosteric site 1), ARG265 (allosteric site 2), and ARG501 (Q-loop) are speculated to be the key residues that causing the SHP2 protein in auto-inhibition conformation. It is hoped that this study will provide clues for the development of the dual allosteric targeted inhibition of SHP2.

Could different direct restoration techniques affect interfacial gap and fracture resistance of endodontically treated anterior teeth?

Objectives

To evaluate different direct restoration techniques on various cavity designs in anterior endodontically treated teeth (ETT).

Materials and methods

Ninety upper central incisors (n = 90) were selected, endodontically treated, and divided into three groups (n = 30) accordingly to the cavity design: minimal endodontic cavity access (group A), endodontic access + mesial class III cavity (group B), and endodontic access + two class III cavities (group C). Three subgroups (n = 10) were then created accordingly to the restoration technique: nano hybrid composite restoration (subgroup a), glass fiber post + dual-cure luting cement (subgroup b), and bundled glass fiber + dual-cure luting cement (subgroup c). Samples underwent micro-CT scan, chewing simulation, and a second micro-CT scan. 3D quantification (mm³) of interfacial gap progression was performed; then, samples underwent fracture resistance test. Data were statistically analyzed setting significance at p < 0.05.

Results

Groups A and B showed significantly lower interfacial gap progression compared with group C. Subgroup b performed significantly better compared with subgroups a and c. Improved fracture strength was reported for group C compared with group A, while both subgroups b and c performed better than subgroup a.

Conclusions

Cavity design significantly influenced interfacial gap progression and fracture resistance. Fiber posts significantly lowered gap progression and improved fracture resistance while bundled fibers only increased fracture resistance. A significant reduction of non-repairable fractures was recorded when fibers were applied.

Clinical relevance

A minimally invasive approach, conserving marginal crests, should be applied whenever possible. Inserting a fiber post is indicated when restoring anterior ETT, in order to reduce gap progression, improve fracture resistance, and avoid catastrophic failures.

The virtual CF clinic: Implications for sputum microbiology

The COVID19 pandemic has shifted the paradigm of how outpatient clinics are delivered within CF care, resulting in a significant reduction of patient visits to CF centres. One consequence of this has been a reduction in the number of sputa/cough swabs that patients submit for routine analysis. This report examines why it is important to maintain optimal sputum microbiology and explores (i). the microbiological efficiency of postal submission of sputum specimens from the community and (ii) the regulatory conditions that must be met through postal submission of respiratory specimens. Virtual clinics have now been established within CF care and it is incumbent on each speciality within the CF MDT to explore ways to nurture and support their individual contribution to the success of the virtual clinic. Within microbiology, adopting innovative approaches to sputum collection in the community and transportation via postal services will allow for continued microbiological vigilance thereby supporting patient safety.

Suicide on Facebook-the tales of unnoticed departure in Bangladesh

Facebook has transformed social communication and offers the opportunity to share personal thoughts to people including suicide ideas, plans and attempts. Suicide after Facebook posts has been reported in different parts of the world and it has become a potential area of research for suicide prevention. The analysis of Facebook posts prior to suicide or Facebook live streaming may help in understanding the etiological factors, patterns of communication and possible prevention approaches for a particular community. However, there is a dearth of evidence about suicide incidents after Facebook posts and Facebook live streaming in low and middle-income countries. This study aims to explore the trends and phenomena of suicide after Facebook posts and live streaming in Bangladesh. We conducted an online search using the Google, Facebook and five daily online newspaper archives from 15th August to 15th September 2019. Two research assistants independently conducted the initial searching to find out people who committed suicide after Facebook posts or live streamed suicide in Bangladesh and documented 21 cases. After further evaluation of each of the 21 cases we confirmed 19 cases that met the selection criteria. All of them were under 35-years of age. We observed sucide after Facebook posts were more common in male(78%) e and students. Hanging was the most frequently used method of suicide followed by poisoning. Their Facebook posts and livestream videos indicated relationship problems, academic stress and mental disorders were the common stressors for their suicide. This study lays the foundation for the future researchers to work on suicidal posts on Facebook in Bangladesh and develop culture-specific, real-time suicide preventive systems using a social media platform.

Hypopituitarism post traumatic brain injury (TBI): review

Post-traumatic hypopituitarism (PTHP) is an important and relatively common complication of TBI (traumatic brain injury). A number of studies have shown that this clinical phenomenon can occur soon after TBI (acute) or later in the chronic phase. Patients with moderate to severe TBI are at a particular risk of developing PTHP. In the acute setting, it is important to monitor patients for hypoadrenalism as this confers a high risk for morbidity and even mortality. The gonadotrophin, growth hormone and TSH deficiencies are better defined in the chronic phase. Untreated PTHP can lead to delayed recovery, impaired rehabilitation and persistent neuropsychiatric symptoms. This review will discuss the frequency and natural history of PTHP and its clinical implications and propose a pathway for investigation and management of this still under-recognised entity.

Adverse Drug Reaction Related Post Detecting Using Sentiment Feature

BACKGROUND

The posts related to Adverse Drug Reaction (ADR) on social websites are believed to be valuable resource for post-marketing drug surveillance. Beyond domain feature, the aim of this study was to find a more effective method to detect ADR related post.

METHODS

We conducted experiment on posts using sentiment features from March 8 to May 20 in 2016 in Shanghai of China. Firstly, the diabetes posts were collected; the 1814 posts were annotated by hand. Secondly, sentiment features set were generated and the χ² (CHI) statistics were used to select feature. Finally, we evaluated the effectiveness of our method using the different feature sets.

RESULTS

By comparing the posts detection performance of different feature sets, using sentiment features by CHI statistics can improve ADR related post detection performance. By comparing the ADR-related group with the non-ADR group, performance of ADR related post detection was better than the performance of non-ADR post detection. We could obtain highest performance owing to introducing sentiment feature and using CHI feature selection technique, and the method was proved to be effective during detecting post related to ADR.

CONCLUSION

By using sentiment feature and CHI feature selection technique, we can get an effective method to detect post related to ADR.

Bond Strength of Fiber Posts to Composite Core: Effect of Surface Treatment With Er,Cr:YSGG Laser and Thermocycling

Introduction: This study aimed to determine the bond strength of fiber post to composite core following surface treatment with Er,Cr:YSGG laser at different powers and sandblasting with and without thermocycling. Methods: In this experimental study, 30 fiber posts (Glassix, Nordin, Switzerland) were randomly divided into 5 groups of sandblasting, no treatment and laser irradiation at 1, 1.5 and 2 W powers. Following composite filling and mounting, 1-mm thick sections were made for pushout bond strength testing. Half of the samples in each group were subjected to thermocycling (n=15). Two-way analysis of variance (ANOVA) was used to analyze the bond strength values. Pairwise comparisons were made using Tukey test (P<0.05). Results: Effect of treatment method on push-out bond strength of fiber post to composite core was significant (P=0.017), while thermocycling had no significant effect on bond strength (P=0.964). Pairwise comparison of surface treatment methods revealed no significant difference in groups with and without thermocycling (P>0.05), but Er,Cr:YSGG laser irradiation with 1 W power yielded significantly higher bond strength than the control group (P=0.01). Conclusion: Irradiation of Er,Cr:YSGG laser at 1 W power increased the bond strength of fiber post to composite core. Thermocycling slightly decreased the bond strength at the fiber postcore interface.

Effect of ferrule on the fracture resistance of mandibular premolars with prefabricated posts and cores

PURPOSE

This study evaluated fracture resistance with regard to ferrule lengths and post reinforcement on endodontically treated mandibular premolars incorporating a prefabricated post and resin core.

MATERIALS AND METHODS

One hundred extracted mandibular premolars were randomly divided into 5 groups (n=20): intact teeth (NR); endodontically treated teeth (ETT) without post (NP); ETT restored with a prefabricated post with ferrule lengths of either 0 mm (F0), 1 mm (F1), or 2 mm (F2). Prepared teeth were restored with metal crowns. A thermal cycling test was performed for 1,000 cycles. Loading was applied at an angle of 135 degrees to the axis of the tooth using a universal testing machine with a crosshead speed of 2.54 mm/min. Fracture loads were analyzed by one-way ANOVA and Tukey HSD test using a statistical program (α=.05).

RESULTS

There were statistical differences in fracture loads among groups (P<.001). The fracture load of F2 (237.7 ± 83.4) was significantly higher than those of NP (155.6 ± 74.3 N), F0 (98.8 ± 43.3 N), and F1 (152.8 ± 78.5 N) (P=.011, P<.001, and P=.008, respectively).

CONCLUSION

Fracture resistance of ETT depends on the length of the ferrule, as shown by the significantly increased fracture resistance in the 2 mm ferrule group (F2) compared to the groups with shorter ferrule lengths (F0, F1) and without post (NP).

Patients with post-essential thrombocythemia and post-polycythemia vera differ from patients with primary myelofibrosis

Prognostic scoring systems for primary myelofibrosis (PMF) are not accurate in patients with post-essential thrombocythemia and post-polycythemia vera myelofibrosis (PET-MF; PPV-MF). Given the paucity of data describing the clinical characteristics, disease course and outcomes of these patients, we sought to describe and compare the clinical characteristics and outcomes of 755 patients with PMF, 181 with PPV-MF, and 163 with PET-MF referred to our institution between 1984 and 2013. The median follow-up was 31 months, and 56% (n=616) patients had died. Over an observation period of 3502 person-years, 11% of patients had progression to AML, with similar rates among groups. The proportion of patients with transfusion dependency (higher in PMF), leukocytosis and systemic symptoms (higher in PPV-MF), and thrombocytopenia (higher in PMF, PPV-MF) differed among groups. Median overall survival (OS) was longest in PET-MF patients (73 mo vs 45 mo (PMF) vs 48 mo (PPV-MF), p <0.001). Stratification of OS by DIPSS was only discriminatory in patients with PMF, and it failed to distinguish higher risk patients with PPV/PET-MF. In multivariate analysis, predictors of inferior OS were higher age, anemia, systemic symptoms, thrombocytopenia, and high peripheral blasts in PMF; age, anemia, and systemic symptoms for PPV-MF; and anemia, peripheral blasts and thrombocytopenia in PET-MF. Although the clinical characteristics of PPV/PET-MF patients are not substantially different from those with PMF, their outcomes differ and prognostic scoring systems for PET/PPV-MF should be improved.

The effects of expressive writing before or after punch biopsy on wound healing

OBJECTIVE

Recent studies have shown that written emotional disclosure (expressive writing) performed in the two weeks prior to wounding improves healing of punch biopsy wounds. In many clinical settings, it would be more practical for patients to perform this intervention after wounding. The aim of this study was to investigate whether expressive writing could speed the healing of punch biopsy wounds if writing was performed after wounds were made.

METHODS

One hundred and twenty-two healthy participants aged between 18 and 55years were randomly allocated to one of four groups in a 2 (intervention) by 2 (timing) design. Participants performed either expressive writing or neutral writing, either before or after receiving a 4mm punch biopsy wound. Wounds were photographed on day 10 (primary endpoint) and day 14 after the biopsy to measure epithelisation. Participants also completed questionnaires on stress and affect two weeks prior to the biopsy, on the day of biopsy and two weeks after biopsy.

RESULTS

There was a significant difference in healing at day 10 between groups, χ²(3, N=97)=8.84, p=0.032. A significantly greater proportion of participants who performed expressive writing before the biopsy had fully reepithelialised wounds on day 10 compared to participants who performed neutral writing either before or after wounding, with no other significant differences between groups. Amongst people who wrote expressively after wounding, those who finished writing over the first 6days were significantly more likely to be healed at 14days than those who finished writing later. There were significant differences in positive and negative affect over the healing period between the pre and post expressive writing groups.

CONCLUSIONS

Expressive writing can improve healing if it is performed prior to wounding. Performing expressive writing after wounding may be able to improve healing depending on the timing of writing and wound assessment. Expressive writing causes affect to worsen followed by subsequent improvement and it is important to consider this in the timing of intervention delivery. Further research with patient groups is required to determine the clinical relevance of these findings.

The Effect of Self-adhesive and Self-etching Resin Cements on the Bond Strength of Nonmetallic Posts in Different Root Thirds

PURPOSE

The purpose of this study was to evaluate the effect of self-adhesive and self-etching resin cements on the bond strength of nonmetallic posts in different root regions.

MATERIALS AND METHODS

Sixty single-rooted human teeth were decoronated, endodontically treated, post-space prepared, and divided into six groups. Glass-fiber (GF) posts (Exacto, Angelus) and fiber-reinforced composite (FRC) posts (EverStick, StickTeck) were cemented with self-adhesive resin cement (Breeze) (SA) (Pentral Clinical) and self-etching resin cement (Panavia-F) (SE) (Kuraray). Six 1-mm-thick rods were obtained from the cervical (C), middle (M), and apical (A) regions of the roots. The specimens were then subjected to microtensile testing in a special machine (BISCO; Schaumburg, IL, USA) at a crosshead speed of 0.5 mm/min. Microtensile bond strength data were analyzed with two-way ANOVA and Tukey's tests.

RESULTS

Means (and SD) of the MPa were: GF/SA/C: 14.32 (2.84), GF/SA/M: 10.69 (2.72), GF/SA/A: 6.77 (2.17), GF/SE/C: 11.56 (4.13), GF/SE/M: 6.49 (2.54), GF/SE/A: 3.60 (1.29), FRC/SA/C: 16.89 (2.66), FRC/SA/M: 13.18 (2.19), FRC/SA/A: 8.45 (1.77), FRC/SE/C: 13.69 (3.26), FRC/SE/M: 9.58 (2.23), FRC/SE/A: 5.62 (2.12). The difference among the regions was statistically significant for all groups (p < 0.05). The self-adhesive resin cement showed better results than the self-etching resin cement when compared to each post (p < 0.05). No statistically significant differences in bond strengths of the resin cements when comparable to each post (p > 0.05).

CONCLUSION

The bond strength values were significantly affected by the resin cement and the highest values were found for self-adhesive resin cement.

Management of post laser in situ keratomileusis ectasia with simultaneous topography guided photorefractive keratectomy and collagen cross-linking

A thirty-nine year old man was referred to our institute due to progressive decreased visual acuity five years after bilateral Laser in situ Keratomileusis (LASIK). Topography revealed signs of post - LASIK ectasia. Patients' left eye was treated with simultaneous Topography Guided Photorefractive Keratectomy (PRK) followed by Corneal Collagen Cross Linking (CXL). Twelve months after the combined procedure both uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) showed significant improvement while topographic findings revealed an improvement of the astigmatic pattern. All higher order aberrations showed a significant decrease twelve months postoperatively. Combined topography guided PRK and corneal cross linking could represent an alternative treatment for post - LASIK ectasia.

Effect of different luting cements on fracture resistance in endodontically treated teeth

INTRODUCTION

The aim of the present study was to evaluate the effect of three types of luting cements used for post cementation on the fracture resistance of endodontically treated maxillary premolars, restored with resin composite.

MATERIALS AND METHODS

One hundred intact single-rooted human maxillary premolars were randomly divided into 5 groups of 20 each. In groups 2-5, post spaces were prepared after root canal treatment and clinical crown reduction up to 1.5 mm above the CEJ. Teeth were divided in groups as follows: Group 1: intact teeth, Group 2: active prefabricated metallic posts (PMP), Group 3: PMP cemented with zinc phosphate luting cement, Group 4: PMP cemented with glass ionomer luting cement and Group 5: PMP cemented with resin luting cement. In groups 2-5 the teeth were restored with resin composite. Following thermocycling, the palatal cusp of each specimen was loaded to compression at an angle of 150˚ to its longitudinal axis at a strain rate of 2 mm/min until fracture occurred. Data were analyzed using one-way ANOVA and a post hoc Tukey test. Chi-square test was used for comparison of failure mode.

RESULTS

There were significant differences in fracture resistance between the test groups (P<0.001). The differences between group 2 with groups 1, 4 and 5 were statistically significant (P<0.05); whereas there were no significant differences in fracture resistance between the two other groups (P>0.05). Furthermore, there were no significant differences in the mode of failure between the 5 groups (P>0.05).

CONCLUSION

Zinc phosphate, glass ionomer and resin luting cements showed similar behaviors and achieved fracture resistance comparable to intact teeth. However, the use of active post (without cement) adversely affected the fracture resistance of root canal treated teeth.