Dentists' knowledge and preference regarding gingival displacement methods

INTRODUCTION

An accurate impression is an essential procedure for fabricating indirect fixed restorations. To achieve a precise final impression, the management of gingival tissue is without doubt a crucial.

AIM

To evaluate the use of different gingival displacement techniques among dental clinicians and to assess their associated knowledge and technique preferences.

METHODS

A self-designed survey was created electronically and sent to a list of dentists. The survey was composed of multiple sections. Participants who stated that they do not use GD methods were asked to answer the survey questions based on their knowledge. Descriptive statistics were generated, andChi-square test was used to examine the association between the different variables.

RESULTS

A total of 188 dentists participated in this study. The majority 144 (76.6%) use GD in their practice. When asked which technique yields a more accurate impression with lower incidence of repeating the impression, 93 (64.6%) reported retraction cord technique with a hemostatic agent results in a higher impression accuracy, while only 14 (9.7%) declared the retraction paste technique as being more accurate.

CONCLUSION

The cordless GD technique is believed to be easier, faster, and less traumatic to the gingival tissues, nevertheless, the outcome of dental impressions is believed to be more predictable with the use of conventional retraction cords and hemostatic medicaments.

Endocrowns Clinical Performance and Patient Satisfaction: A Randomized Clinical Trial of Three Monolithic Ceramic Restorations

PURPOSE

The purpose of this randomized, double-blind, clinical trial was to assess the survival of endocrowns made from three different monolithic ceramic materials, and to evaluate patient satisfaction.

MATERIALS AND METHODS

Fifty-three patients (sixty root canal treated molar teeth) were enrolled. Teeth were prepared to a flat butt-joint margin and randomly divided between three material groups: lithium disilicate-reinforced glass-ceramic, monolithic zirconia and polymer infiltrated hybrid ceramic. Predefined cementation protocols were used. Clinical assessment using modified United States Public Health Service (USPHS) criteria was carried out after two years by two independent clinicians blinded to the material used. Radiographic examination was conducted to check for the presence of caries, excess cement, and periapical infection. Statistical analysis was performed using the Kruskal Wallis and Wilcoxon signed-rank tests as well as the Kaplan-Meier survival estimate.

RESULTS

Forty-eight patients were available for assessment after 2 years (recall rate 90.6%). The overall Kaplan-Meier survival estimate among all groups was 90.9% with no statistically significant difference between the groups (p = 0.17). Three zirconia endocrowns debonded after 9, 10 and 13 months (82.4% survival rate), while 2 hybrid ceramic endocrowns chipped/fractured (89.5% survival rate). Lithium disilicate endocrowns had a 100% survival rate. The Kruskal Wallis test revealed no statistically significant difference between the groups in the USPHS criteria ratings and the radiographic assessment (P>0.05). Patient satisfaction ranged from 82.3% in the zirconia group to 100% in both the lithium disilicate and hybrid ceramic groups.

CONCLUSIONS

Endocrowns provide a predictable option for the restoration of endodontically treated molar teeth in the short term. Lithium disilicate-reinforced ceramic had fewer complications and required less intervention compared with zirconia and hybrid ceramics. Long-term follow-up is required to substantiate these study results.

Impact of COVID-19 pandemic on dental education: online experience and practice expectations among dental students at the University of Jordan

BACKGROUND

The quarantine associated with the COVID-19 pandemic forced dental schools to suspend their clinical training and to shift to distant learning methods. The aim of this study is to investigate the impact of quarantine on the self-perceived preparedness of dental graduates and to explore the efficacy of online education from students' perspectives.

METHODS

The questionnaire distributed to dental students comprised of two main sections. The first part covered the online education experience, and the second part measured the level of self-perceived preparedness for a range of cognitive, communication and professional skills.

RESULTS

The survey yielded a response rate of 72%. The majority of students (77%) agreed that they missed educational experiences as a result of the lockdown. More than half of them felt less motivated to follow-up with distant e-learning and believed that online assessment is not a good method for evaluation. A high percentage of the students (66%) thought that online group discussions had a positive value while 67% preferred online lectures compared to theatre lectures. Majority of students particularly 5th year (78.7%) (p < 0.001) stated that the quarantine increased their collaboration with their colleagues. According to 87% of students, the experience most negatively affected was their clinical training. In general, students showed satisfactory self-perceived preparedness related to a range of attributes and professional skills.

CONCLUSIONS

The data showed that students partially appreciated the online system, whereas they did not consider it a substitute for face to face clinical practice. The overall self-perceived preparedness level was promising; however students had reservations regarding independent practice following graduation.

Dental students' experience and perceived confidence level in different restorative procedures

PURPOSE

Graduating confident students who are able to flourish and develop in their future careers is an importance outcome of the dental education. This study aims to evaluate self-perceived level of confidence of fifth-year dental students in different restorative-related tasks and the relationship between their clinical training and its corresponding confidence.

METHODS

Fifth-year graduate dental students (n = 202) were asked to fill a questionnaire that rated their level of confidence in different clinical restorative dentistry tasks. Additionally, they were asked about the number of times they performed tasks prior to attempting the equivalent competency and in which sub-specialty they felt the most confident.

RESULTS

Completed responses were received from 120 students giving a response rate of 59%. Students felt the most prepared and confident in direct restorations and simple endodontic treatment, and they seemed less confident in indirect restorations and complex endodontic treatment. Regarding the steps of indirect restorations, students expressed least confidence in crown preparation compared to impression making and try-in procedures (P < .05). Students rated their confidence highest in operative dentistry, followed by endodontics and lastly fixed prosthodontics.

CONCLUSION

The results highlight the areas in which students exhibit the least confidence. Enhancement of student clinical skills and directed exposure is necessary to raise the level of perceived confidence which will reflect positively on their current and future professional performance.

Self-perceived preparedness of dental school graduates and the impact of COVID-19 pandemic on their confidence.. [DOI: 10.21203/rs.3.rs-49483/v3]

Background. To study self-perceived preparedness of dental school graduates and the impact of COVID-19 on their preparedness. Method. An online survey was designed and sent electronically to students who were graduating in 2020, dentists who graduated in 2019 and were doing their prelicensure training, and dentists who graduated before 2019. Four- point Likert scale was used to assess participants’ perception.Results. There were 209 participants responded to the online questionnaire. The mean total preparedness score (TPS) for the 209 participants was 97.6 (SD ±9.7) with a range of 69 to 120. The mean TPS of the different classes of participants was 99.5 for the class graduated before 2019, 98.1 for the 2020 class, and 95.1 for the 2019 class. Participants felt they are confident and extremely confident doing the majority of the required competencies. Weakness was mainly reported in surgical extraction for 2020 graduates due to the 8 weeks loss of their training. COVID-19 had considerable impact on 59.7% of the participants and marginal to no impact on 40.3%. The highest prevalence of those who thought it had some to severe impact on their confidence were those who graduated in year 2019 (73.4%).Conclusions. The graduates of University of Jordan felt confident in performing the majority of general dentistry procedures. COVID-19 pandemic negatively impacted the confidence of all the classes of participants even those graduated before 2019.

Self-perceived preparedness of dental school graduates and the impact of COVID-19 pandemic on their confidence.. [DOI: 10.21203/rs.3.rs-49483/v2]

Background. To study self-perceived preparedness of dental school graduates and the impact of COVID-19 on their preparedness. Method. An online survey was designed and sent electronically to students who are graduating in 2020, dentists who graduated in 2019 and doing their prelicensure training, and dentists who graduated before 2019. Four- point Likert scale was used to assess participants’ perception. Results. There were 209 participants responded to the online questionnaire. The mean total preparedness score (TPS) for the 209 participants was 97.6 (SD ±9.7) with a range of 69 to 120. The mean TPS of the different classes of participants was 99.5 for the class graduated before 2019, 98.1 for the 2020 class, and 95.1 for the 2019 class. Participants felt they are confident and extremely confident doing the majority of the required competencies. Weakness was mainly reported in surgical extraction for 2020 graduates due to the 8 weeks loss of their training. COVID-19 has considerable impact on 59.7% of the participants and marginal to no impact on 40.3%. The highest prevalence of those who thought it had some to severe impact on their confidence were those who graduated in year 2019 (73.4%). Conclusions. The graduates of University of Jordan felt confident in performing the majority of general dentistry procedures. COVID-19 pandemic negatively impacted the confidence of all the classes of participants even those graduated before 2019.

Self-perceived preparedness of dental school graduates and the impact of COVID-19 pandemic on their confidence.. [DOI: 10.21203/rs.3.rs-49483/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

BackgroundTo study self-perceived preparedness of dental school graduates and the impact of COVID-19 on their preparedness.MethodAn online survey was designed and sent electronically to students who are graduating in 2020, dentists who graduated in 2019 and doing their prelicensure training, and dentists who graduated before 2019. Four- point Likert scale was used to assess participants’ perception.Results209 participants responded to the online questionnaire. The mean total preparedness score (TPS) for the 209 participants was 97.6 (SD ± 9.7) with a range of 69 to 120. The mean TPS of the different classes of participants was 99.5 for the class graduated before 2019, 98.1 for the 2020 class, and 95.1 for the 2019 class. Participants felt they are confident and extremely confident doing the majority of the required competencies. Weakness was mainly reported in surgical extraction for 2020 graduates due to the 8 weeks loss of their training. COVID-19 has considerable impact on 59.7% of the participants and marginal to no impact on 40.3%. The highest prevalence of those who thought it had some to severe impact on their confidence were those who graduated in year 2019 (73.4%). Of the participants 95.2% agreed that problem-based learning is a good educational tool and 58.5% agreed that competency-based assessment is a good educational and grading tool.ConclusionsThe graduates of University of Jordan felt confident in performing the majority of general dentistry procedures. COVID-19 pandemic negatively impacted the confidence of all the classes of participants even those graduated before 2019.

Impact of COVID-19 pandemic on dental academia. Students’ experience in online education and expectations for a predictable practice.. [DOI: 10.21203/rs.3.rs-54480/v1]

AbstractBackground: The quarantine associated with the COVID-19 pandemic forced dental schools to suspend their clinical training and to shift to distant learning methods. The aim of this study is to investigate the impact of COVID-19 quarantine on the preparedness of dental graduates and to explore the efficacy and limitations of online education from students’ perspectives. Methods: the questionnaire distributed to dental students comprised of two main sections; first part covered the online education experience and the second part measured the level of preparedness for a range of cognitive, communication and professional skills. Results: the survey yielded a response rate of 72%. The majority of students (77%) agreed that they missed educational experiences as a result of the lockdown. More than half of them felt less motivated in following-up with distant e-learning and believed that online assessment is not a good method for evaluation. A high percentage of the students (66%) thought that online group discussions has a positive value whilst 67% preferred online lectures compared to theatre lectures. Majority of students particularly 5th year (78.7%) (p<0.001) stated that the quarantine increased their collaboration with their colleagues. According to 87% of students, the experience most negatively affected was their clinical training.In general, students showed satisfactory preparedness related to a range of attributes and professional skills, however, nearly two-thirds of them prefer to be mentored and favor a structured year of residence. Conclusions: Data showed that students partially appreciated the online system, whereas they did not consider it a substitute for face to face clinical practice. The overall preparedness level was promising, however, some skills regarding evidence-based practice need consolidation. Students had reservations regarding independent practice following graduation.

Esthetic outcome of immediately placed and nonfunctionally loaded implants in the anterior maxilla utilizing a definitive abutment: A pilot clinical trial

Background:

Immediate dental implants placement and loading utilizing definitive abutments might save time and cost when an esthetic final result is anticipated. The objective of this prospective clinical trial was to evaluate the esthetic outcome of immediate implantation and immediate nonfunctional loading utilizing definitive abutments, with and without bony substitutes filling the peri-implant gap.

Materials and Methods:

In this clinical trial study a total of 11 implants were placed utilizing a flapless immediate post extraction approach in the maxilla (second premolar to second premolar). Atraumatic extraction was performed and implants were immediately placed. The gap was either left without grafting or filled with particulate bone material. Immediate nonfunctional loading was performed utilizing a definitive abutment. The pink esthetic scores (PESs) were assessed preoperatively, at 1- and 2-year follow-up periods. Dental casts were obtained at respective time intervals; scanned, registered, and closest point distances were measured. For all statistical tests, value of P = 0.05 was set as a statistical significance level.

Results:

The mean of PES at baseline was 9.4 ± 1.69, at 1 year was 9.5 ± 2.07, at 2 years was 10.2 ± 2.75, for the graft group 10.3 ± 2.8, and for nongrafting group was 10.2 ± 2.59. There were no statistically significant differences in PESs at baseline when compared to 1- and 2-year intervals, and for grafting group versus nongrafting group (P = 0.24). Distances between the two time points for all cases were <1 mm in all reference planes.

Conclusion:

Immediate placement and nonfunctional loading utilizing a definitive abutment appear to result in a stable result as far as esthetic outcome and alveolar process sufficiency are concerned.

A multi-center retrospective assessment of monolithic zirconia restorations on posterior teeth and implants

Objective: the purpose of this multicenter retrospective study was to report on survival, success, and complication rates in monolithic zirconia restorations on teeth and implants. Materials and Methods: data on 671 monolithic zirconia restorations was collected by five prosthodontists from three different specialty practice centers, including a dental school and two private practice centers. Restorations included single crowns and multiple-unit fixed dental prostheses on teeth and implants in the posterior area (premolar and molars). Follow-up time was up to 62 months. Results: mean follow-up time was 28.1±12.9 months. A total of 671 units, 534 single crowns, and 137 multi-unit restorations. Cumulative survival and success rates at 5 years were 97.4%, and 93.8% respectively. Complications presented in 11 restorations out of 671 and included: decementation, abutment screw loosening, restoration crack, restoration fracture, and tooth fracture. No significant differences were observed between tooth-supported and implant-supported restoration (p=0.42), single crowns and multiple-unit restorations (p=0.07), bruxers and non-bruxers (p=0.57). Patients with group function occlusal scheme had significantly less survival rates (p=0.001). Conclusion: the use of monolithic zirconia for restorations on the posterior teeth and implants seems to be promising as it provides a durable solution with a low rate of complications.

Bond strength of self-adhesive resin cements to tooth structure

OBJECTIVES

The aim of this study was to evaluate the strength of the bond between newly introduced self-adhesive resin cements and tooth structures (i.e., enamel and dentin).

METHODS

Three self-adhesive cements (SmartCem2, RelyX Unicem, seT SDI) were tested. Cylindrical-shaped cement specimens (diameter, 3 mm; height, 3 mm) were bonded to enamel and dentin. Test specimens were incubated at 37 °C for 24 h. The shear bond strength (SBS) was tested in a Zwick Roll testing machine. Results were analyzed by one-way ANOVA and t-test. Statistically significant differences were defined at the α = 0.05 level. Bond failures were categorized as adhesive, cohesive, or mixed.

RESULTS

The SBS values ranged from 3.76 to 6.81 MPa for cements bonded to enamel and from 4.48 to 5.94 MPa for cements bonded to dentin (p > 0.05 between surfaces). There were no statistically significant differences between the SBS values to enamel versus dentin for any given cement type. All cements exhibited adhesive failure at the resin/tooth interface.

CONCLUSIONS

Regardless of their clinical simplicity, the self-adhesive resin cements examined in this study exhibit limited bond performance to tooth structures; therefore, these cements must be used with caution.

Shear bond strength of self-adhesive resin cements to base metal alloy

STATEMENT OF PROBLEM

Many self-adhesive cements have been introduced in the past few years, with little or no data regarding their clinical performance. This study investigated the shear bond strength of some recently introduced self-adhesive resin cements.

PURPOSE

The purpose of this study was to evaluate the shear bond strength of self-adhesive and conventional resin-based cements to a base metal alloy.

MATERIAL AND METHODS

Four groups (10-12 each) that comprised 3 self-adhesive cements (SmartCem2; RelyX Unicem; seT SDI) and a conventional resin-based cement (RelyX ARC) were tested. Cylindrical cement specimens (diameter, 3 mm; height, 3 mm) were applied to nickel-free base metal alloy (Sheradent) disks with a diameter of 12 mm, and the surface was treated with airborne-particle abrasion of 50 μm aluminum oxide. The metal disks were fixed in brass molds specifically designed for the shear bond test device. Test specimens were incubated at 37°C for 24 hours and then the shear bond was tested with a Zwick Roll testing machine at a 0.8 mm/min cross-head speed. In addition, bond failures were investigated and categorized as adhesive, cohesive, or mixed. Shear bond strengths were calculated by dividing the maximum debonding force over the cross-sectional area of each specimen. One-way ANOVA and the Tukey (honestly significant difference) post hoc test were used to test statistical significant differences among the groups (α=.05).

RESULTS

Statistical analysis showed significant differences among different resin cements (F=14.34, P<.001). The highest mean shear bond strength was observed for SmartCem2 (14.18 MPa), and the lowest was reported for seT (3.52 MPa). The observed failure mode in all the materials was adhesive in nature, which occurred at the resin-metal interface.

CONCLUSIONS

The early bond strength of self-adhesive resin cements varied significantly among the tested materials. SmartCem2 showed the highest bond strength, which was 4 times the strength observed for seT SDI.

Students' opinions and attitudes after performing a dental OSCE for the first time: a Jordanian experience

This study at the Faculty of Dentistry, University of Jordan investigated and evaluated students' attitudes and opinions after attempting a dental objective structured clinical examination (OSCE) for the first time. The OSCE consisted of sixty-seven stations for fourth-year dental students. After the exam, students were asked to voluntarily complete a questionnaire designed to evaluate their attitudes and opinions about the exam. Of the 134 students who participated in the OSCE, 93.2 percent completed the questionnaire; 43.4 percent said they found the exam difficult and 56.6 percent found it easy (p=0.147). Seventy percent reported that the exam was objective, while 30 percent did not (p<0.001); 65.5 percent indicated that it was a better test than traditional patient-based tests, whereas 34.5 percent did not (p<0.001). Sixty-eight percent stated that there were too many stations, while 30.9 percent stated the number of stations was appropriate and 0.8 percent stated there were too few (p<0.001). Of these respondents, 75.6 percent reported the exam was organized, whereas 21.1 percent said the exam was not very well organized and 3.3 percent said the exam was not organized at all (p<0.001). Overall, the students responded that the OSCE was able to test their clinical judgment and skills and it was a better method for evaluating their clinical skills; most preferred to have such tests in the future. Although the students reported the exam had too many stations, they perceived that it was well organized and that the time allocated for each station was appropriate. These dental students perceived that the OSCE was a suitable method to test operative dentistry clinical judgment and skills.

Dentistry a second time?

INTRODUCTION

Dentistry in Jordan is an attractive profession due to the high social standard it provides. This study aimed to investigate whether dentists would choose dentistry again and whether their professional expectations would change after years of practice. Of special interest were possible differences according to gender, age, degree and place of work.

METHODS

A self-completion questionnaire was filled by a stratified random sample of 355 dentists in Jordan using closed questions. The questionnaire included professional, social and economic factors that influenced people's choice of dentistry and whether they would choose it again and the reasons for that.

RESULTS

The results showed that 52% of dentists who returned the questionnaire had dentistry as their first choice; the most important determining factor was the dentist's grades in the general secondary education. Fifty-two per cent stated that they would not choose it for the second time, the main reason being the health problems acquired through the profession and the low income. Helping others and the social standard dentistry provides were the main reasons given for dentists to choose dentistry again.

CONCLUSION

We report that more than half of the dentists included in this study would not 'choose dentistry again' as their profession regardless of age, gender and degree. This is mainly due to health problems acquired and the low income. We found that job satisfaction is highly affected by the workplace, and that more females are dissatisfied by the profession. This suggests that cultural background strongly affects the career decision.

Photoentrainment and pupillary light reflex are mediated by distinct populations of ipRGCs

Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and regulate a wide array of light-dependent physiological processes^1–11. Genetic ablation of ipRGCs eliminates circadian photoentrainment and severely disrupts the pupillary light reflex (PLR)^12,13. Here we show that ipRGCs consist of distinct subpopulations that differentially express the Brn3b transcription factor, and can be functionally distinguished. Brn3b-negative M1 ipRGCs innervate the suprachiasmatic nucleus (SCN) of the hypothalamus, whereas Brn3b-positive ipRGCs innervate all other known brain targets, including the olivary pretectal nucleus. Consistent with these innervation patterns, selective ablation of Brn3b-positive ipRGCs severely disrupts the PLR, but does not impair circadian photoentrainment. Thus, we find that molecularly distinct subpopulations of M1 ipRGCs, which are morphologically and electrophysiologically similar, innervate different brain regions to execute specific light-induced functions.

Impaired Masking Responses to Light in Melanopsin‐Knockout Mice

There are two ways in which an animal can confine its behavior to a nocturnal or diurnal niche. One is to synchronize an endogenous clock that in turn controls the sleep-wake cycle. The other is to respond directly to illumination with changes in activity. In mice, high illumination levels suppress locomotion (negative masking) and low illumination levels enhance locomotion (positive masking). To investigate the role of the newly discovered opsin-like protein melanopsin in masking, we used 1 h and 3 h pulses of light given in the night, and also a 3.5:3.5 h light-dark (LD) cycle. Mice lacking the melanopsin gene had normal enhancement of locomotion in the presence of dim lights but an impaired suppression of locomotion in the presence of bright light. This impairment was evident only with lights in the order of 10 lux or brighter. This suggests that melanopsin in retinal ganglion cells is involved in masking, as it is in pupil contraction and phase shifts. Melanopsin is especially important in maintaining masking responses over long periods.

Prevalence, association, and sexual dimorphism of Carabelli's molar and shovel incisor traits amongst Jordanian population

INTRODUCTION

The correlation between dental morphological traits can be used as an indicator to show major ethnic differences. Therefore, this study investigated the prevalence of Carabelli's molar and shovel incisor traits and tested their association and sexual dimorphism in Jordanian population.

MATERIAL AND METHODS

Three hundred subjects of school children at their 10th grade and of 15.5-year as an average age were involved. Alginate impressions for the maxillary arch were taken, poured, and casts were then trimmed. The selected accurate casts were of 132 male- and 155 female-students. The examined morphologic traits were Carabelli's trait on the maxillary first and second molars and shovel-shaped incisors. The relationship between different traits was investigated by Nonparametric Correlation analysis and Independent Sample t test was used to test sexual dimorphism in trait expression.

RESULTS

The prevalence of Carabelli's trait in maxillary first molar and shovel trait in maxillary central incisor was relatively high (65.0 % and 53.0 %, respectively). The prevalence of Carabelli's trait on maxillary second molars was 3.8 %. Nonparametric Correlations revealed a strongest positive correlation between Carabelli's trait on maxillary first molar and shovel trait in males (P = 0.005). Significant sexual dimorphism was only found in the prevalence of Carabelli's trait on maxillary first molar (P = 0.013) and shovel trait (P = 0.038).

CONCLUSIONS

The Jordanian Population had comparatively high prevalence of Carabelli's molar and shovel incisor traits. There was a positive association between Carabelli's trait on maxillary first molar and shovel trait in males. Sexual dimorphism was evident in Carabelli's trait on maxillary first molar and shovel trait.

Multiple photoreceptors contribute to nonimage-forming visual functions predominantly through melanopsin-containing retinal ganglion cells

In the absence of functional rod and cone photoreceptors, mammals retain the ability to detect light for a variety of physiological functions such as circadian photoentrainment and pupillary light reflex. This is attributed to a third class of photoreceptors, the intrinsically photosensitive retinal ganglion cells that express the photopigment melanopsin. Even though in the absence of rods and cones, mammals retain the ability to detect light for various nonimage-forming visual functions, rods and cones can compensate for the absence of the melanopsin protein in nonvisual light-dependent physiological behaviors. Several studies have addressed the relative contribution of each photoreceptor type to nonimage-forming visual functions; however, a comprehensive model for these interactions is far from complete. Under conditions where melanopsin-containing retinal ganglion cells were genetically ablated, image formation is maintained, whereas circadian photoentrainment and pupillary light reflex are severely impaired. The findings indicate that multiple photoreceptors contribute to nonimage-forming visual functions through signaling via melanopsin-containing retinal ganglion cells. Future studies will aim to determine more quantitatively the relative contributions of each retinal photoreceptor in signaling light for nonimage-forming visual functions.

Effects of 58S sol–gel glasses on the temporal expression of bone markers during mouse osteoblastic differentiation

Previous studies have shown that bioactive glasses can support osteoblastic growth and differentiation in vitro as well as in vivo. More recently, a new category of sol-gel glasses has been developed with enhanced bioactivity and open pores enclosed in a mesoporous matrix. In our study, we investigated the effect of 58S sol-gel glasses on the growth and differentiation of mouse calvaria osteoblasts. Two types of granules were used: 58S sol-gel granules and 60S inert glasses used as control. Phase contrast microscopy showed that cells proliferated and formed mineralized bone nodules in both cultures. However, this phenomenon occurred earlier and to a higher degree in cultures with 58S sol-gel glasses. Northern blot analysis of the expression of osteoblastic markers revealed that osteoblasts retained their phenotype in both types of cultures. Interestingly, stimulation of alkaline phosphatase, bone sialoprotein, and osteocalcin was noticed at day 18 in sol-gel cultures when compared with that in control. These data confirm that 58S bioactive glasses are capable of supporting the growth and maturation of primary mouse osteoblasts. In addition, it was shown that 58S glasses affected the gene-expression profile, causing an up-regulation of the major bone markers. These results indicated that 58S sol-gel glasses appeared as suitable candidates for osteoblast scaffolds in the field of bone tissue engineering.

Melanopsin-dependent photoreception provides earliest light detection in the mammalian retina

BACKGROUND

The visual system is now known to be composed of image-forming and non-image-forming pathways. Photoreception for the image-forming pathway begins at the rods and cones, whereas that for the non-image-forming pathway also involves intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. In the mouse retina, the rod and cone photoreceptors become light responsive from postnatal day 10 (P10); however, the development of photosensitivity of the ipRGCs remains largely unexplored.

RESULTS

Here, we provide direct physiological evidence that the ipRGCs are light responsive from birth (P0) and that this photosensitivity requires melanopsin expression. Interestingly, the number of ipRGCs at P0 is over five times that in the adult retina, reflecting an initial overproduction of melanopsin-expressing cells during development. Even at P0, the ipRGCs form functional connections with the suprachiasmatic nucleus, as assessed by light-induced Fos expression.

CONCLUSIONS

The findings suggest that the non-image-forming pathway is functional long before the mainstream image-forming pathway during development.

Diurnal mice (Mus musculus) and other examples of temporal niche switching

Examples are presented of nocturnal animals becoming diurnal or vice versa as a result of mutations, genetic manipulations, or brain lesions. Understanding these cases could give insight into mechanisms employed when switches of temporal niche occur as part of the life cycle, or in response to circumstances such as availability of food. A two-process account of niche switching is advocated, involving both a change in clock-controlled outputs and a change in the direct response to light (i.e. masking). An emerging theme from this review is the suggestion that retinal inputs have a greater role in switching than suspected previously.

The modulation of tissue-specific gene expression in rat nasal chondrocyte cultures by bioactive glasses

Since bone repair may occur, following endochondral ossification, we have investigated the behaviour of chondrocytes isolated from nasal septum cartilage of foetal rats and cultured up to 21 days in the presence of a melt-derived bioactive glass (Bioglass 45S5) and a less reactive glass with 60 wt% silica content (60S). In both cultures, chondrocytes proliferate and form typical cartilaginous nodules on day 5 of cultures. However, on day 12, the nodules in contact with 45S5 granules became darker than in 60S cultures, corresponding to the emergence of matrix biomineralization. Transmission electron microscopy showed a collagen-rich matrix composed of densely packed fibres and mineralized foci formed of needle-shaped crystals in contact with an electron-dense layer located at the periphery of the material. The specific activity of alkaline phosphatase was significant higher in 45S5 cultures on day 15 than in 60S cultures. Real time RT-PCR was used to monitor gene expression levels of specific chondrogenic markers. The transcription factor Sox9 was expressed throughout the culture period, but with no significant differences between the two kinds of cultures. In contrast, Runx2 expression was higher in experiment cultures on day 12. Type II collagen mRNA and aggrecan, showed an almost similar expression pattern with a strong expression at the beginning of cultures but higher in experiment cultures. Indian hedgehog was strongly expressed between day 9 and 12 with a significant stimulation in 45S5 cultures. Similarly, type X collagen mRNA seemed to be up-regulated in 45S5 cultures on day 20. In conclusion, this study shows hat 45S5 Bioglass has the ability to support the growth of chondrocytes and to stimulate some chondrogenic molecular markers.

Potential of biomimetic surfaces to promote in vitro osteoblast-like cell differentiation

Bioactive glasses, osteoproductive materials, have received considerable attention as bone graft substitutes in the treatment of bony defects. More recent strategies for achieving a predictable periodontal regeneration include the use of enamel matrix proteins, due to their role in the formation of bone tissue. The aim of our study is to examine the effects of these materials on the proliferation and differentiation of the mouse preosteoblastic cell line MC3T3-E1. Cells were cultured up to 28 days in contact with three types of granules: Bioglass 45S5 granules (BG), 45S5 granules coated with enamel matrix proteins (Emdogain) (BG/EMD), and a less reactive glass used as a control (60S). Phase contrast microscopic observations have shown that all substrates supported the growth of osteoblastic cells. Zones of differentiation were observed at an earlier stage in cultures of BG and BG/EMD. TEM observations revealed ultrastructural features very close to what is observed in vivo during intramembranous ossification with a direct bone apposition on the bioactive glasses. Total protein production was higher in the cultures with BG and BG/EMD. Northern Blot analysis revealed a stimulation of the transcription factor Cbfa1/Runx2 at day 13 in cultures of BG when compared to the two other cultures. Bone sialoprotein (early marker of differentiation) and osteocalcin (marker of late-stage differentiation) expression was increased in cultures with BG and BG/EMD when compared to 60S. Taken together, our findings indicate that Bioglass alone or combined with Emdogain, have the ability to support the growth of osteoblast-like cells in vitro and to promote osteoblast differentiation by stimulating the expression of major phenotypic markers. In addition, we noticed that the bioactive granules coated with Emdogain revealed significantly higher protein production than the bioactive granules alone at day 20.

Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice

In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive. Furthermore, pupil reflex, light-induced phase delays of the circadian clock and period lengthening of the circadian rhythm in constant light are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells. We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod-cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.

The biomimetics of bone: engineered glass-ceramics a paradigm for in vitro biomineralization studies

In this study, we investigated the behavior of fetal rat osteoblasts cultured up to 23 days on a bioactive apatite-wollastonite glass-ceramic (AW) and on the same material on which a carbonated apatite layer was formed by a biomimetic process (AWa). The specific activity of alkaline phosphatase activity was about 30% increased on AWa compared to AW disks at the last day of culture. Scanning electron microscopic (SEM) observations of the material surfaces after scrapping off the cell layers revealed that mineralized bone nodules remained attached to both surfaces but in larger numbers on AWa. The AWa/bone interfaces were also analyzed after fracturing the disks and by transmission electron microscopy (TEM). All these results indicated the importance of the surface composition in supporting differentiation of osteogenic cells and the subsequent apposition of bone matrix. Furthermore, prefabrication of a biological apatite layer by a biomimetic method could improve our knowledge of biomineralization processes and could find application as bone-repairing material.

Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice

In the mammalian retina, a small subset of retinal ganglion cells (RGCs) are intrinsically photosensitive, express the opsin-like protein melanopsin, and project to brain nuclei involved in non-image-forming visual functions such as pupillary light reflex and circadian photoentrainment. We report that in mice with the melanopsin gene ablated, RGCs retrograde-labeled from the suprachiasmatic nuclei were no longer intrinsically photosensitive, although their number, morphology, and projections were unchanged. These animals showed a pupillary light reflex indistinguishable from that of the wild type at low irradiances, but at high irradiances the reflex was incomplete, a pattern that suggests that the melanopsin-associated system and the classical rod/cone system are complementary in function.

Behaviour of moderately differentiated osteoblast-like cells cultured in contact with bioactive glasses

Bioactive glasses have been shown to stimulate osteogenesis both in vivo and in vitro. However, the molecular mechanisms underlying this process are still poorly understood. In this study, we have investigated the behaviour of osteoblast-like cells (MG63), cultured in the presence of bioglass particles. Three types of granules were used: 45S5 bioactive glass, 45S5 granules preincubated in tris buffer and 60S non-reactive glass, used as control. Phase contrast microscopy permitted step-by-step visualization of cell cultures in contact with the particles. Ultrastructural observations of undecalcified sections revealed direct contacts of the cells and an electron-dense layer located at the periphery of the material. Protein synthesis was evaluated biochemically and showed a gradual increase throughout the culture time in the three types of cultures. Alkaline phosphatase was detected in situ, in clusters of packed cells either in contact with the material or in the background cell layer. Semi-quantitative RT-PCR analysis of the main osteoblastic markers showed that gene expression was maintained in all three cultures. The fact that osteocalcin was not detected, supports the fact that the MG63 cell line is composed of less differentiated osteogenic cells rather than mature osteoblasts. We also demonstrated for the first time in this cell line, the expression of Msx-2, Dlx-3 and Dlx-7 homeogenes, known to regulate in vivo foetal skeletogenesis as well as adult skeletal regeneration. However, no significant differences could be recognised in the expression pattern of bone markers between the three types of cultures. Yet these preliminary results indicate that bioactive glasses provided a suitable environment for the growth and proliferation of osteoblasts in vitro, since no drastic changes in phenotype expression of pre-osteoblasts was noted.

Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity

The primary circadian pacemaker, in the suprachiasmatic nucleus (SCN) of the mammalian brain, is photoentrained by light signals from the eyes through the retinohypothalamic tract. Retinal rod and cone cells are not required for photoentrainment. Recent evidence suggests that the entraining photoreceptors are retinal ganglion cells (RGCs) that project to the SCN. The visual pigment for this photoreceptor may be melanopsin, an opsin-like protein whose coding messenger RNA is found in a subset of mammalian RGCs. By cloning rat melanopsin and generating specific antibodies, we show that melanopsin is present in cell bodies, dendrites, and proximal axonal segments of a subset of rat RGCs. In mice heterozygous for tau-lacZ targeted to the melanopsin gene locus, beta-galactosidase-positive RGC axons projected to the SCN and other brain nuclei involved in circadian photoentrainment or the pupillary light reflex. Rat RGCs that exhibited intrinsic photosensitivity invariably expressed melanopsin. Hence, melanopsin is most likely the visual pigment of phototransducing RGCs that set the circadian clock and initiate other non-image-forming visual functions.

Identification of specific mRNAs affected by treatments producing long-term facilitation in Aplysia

Neural correlates of long-term sensitization of defensive withdrawal reflexes in Aplysia occur in sensory neurons in the pleural ganglia and can be mimicked by exposure of these neurons to serotonin (5-HT). Studies using inhibitors indicate that transcription is necessary for production of long-term facilitation by 5-HT. Several mRNAs that change in response to 5-HT have been identified, but the molecular events responsible for long-term facilitation have not yet been fully described. To detect additional changes in mRNAs, we investigated the effects of 5-HT (1.5 hr) on levels of mRNA in pleural-pedal ganglia using in vitro translation. Four mRNAs were affected by 5-HT, three of which were identified as calmodulin (CaM), phosphoglycerate kinase (PGK), and a novel gene product (protein 3). Using RNase protection assays, we found that 5-HT increased all three mRNAs in the pleural sensory neurons. CaM and protein 3 mRNAs were also increased in the sensory neurons by sensitization training. Furthermore, stimulation of peripheral nerves of pleural-pedal ganglia, an in vitro analog of sensitization training, increased the incorporation of labeled amino acids into CaM, PGK, and protein 3. These results indicate that increases in CaM, PGK, and protein 3 are part of the early response of sensory neurons to stimuli that produce long-term facilitation, and that CaM and protein 3 could have a role in the generation of long-term sensitization.

A developmental gene (Tolloid/BMP-1) is regulated in Aplysia neurons by treatments that induce long-term sensitization

Long-term sensitization training, or procedures that mimic the training, produces long-term facilitation of sensory-motor neuron synapses in Aplysia. The long-term effects of these procedures require mRNA and protein synthesis (Montarolo et al., 1986; Castellucci et al., 1989). Using the techniques of differential display reverse transcription PCR (DDRT-PCR) and ribonuclease protection assays (RPA), we identified a cDNA whose mRNA level was increased significantly in sensory neurons by treatments of isolated pleural-pedal ganglia with serotonin for 1.5 hr or by long-term behavioral training of Aplysia. The effects of serotonin and behavioral training on this mRNA were mimicked by treatments that elevate cAMP. The aplysia mRNA increased by serotonin and behavioral training was 41-45% identical to a developmentally regulated gene family which includes Drosophila tolloid and human bone morphogenetic protein-1 (BMP-1). Both tolloid and BMP-1 encode metalloproteases that might activate TGF-beta (transforming growth factor beta)-like molecules or process procollagens. Aplysia tolloid/BMP-1-like protein (apTBL-1) might regulate the morphology and efficacy of synaptic connections between sensory and motor neurons, which are associated with long-term sensitization.