Hydrolysis of amelogenin by matrix metalloprotease-20 accelerates mineralization in vitro

In the following respects, tooth enamel is a unique tissue in the mammalian body: (a) it is the most mineralized and hardest tissue in it comprising up to 95 wt% of apatite; (b) its microstructure is dominated by parallel rods composed of bundles of 40–60 nm wide apatite crystals with aspect ratios reaching up to 1:10,000 and (c) not only does the protein matrix that gives rise to enamel guides the crystal growth, but it also conducts its own degradation and removal in parallel. Hence, when mimicking the process of amelogenesis in vitro, crystal growth has to be coupled to proteolytic digestion of the amelogenin assemblies that are known to play a pivotal role in conducting the proper crystal growth. Experimental settings based on controlled and programmable titration of amelogenin sols digested by means of MMP-20 with buffered calcium and phosphate solutions were employed to imitate the formation of elongated, plate-shaped crystals. Whilst amelogenin can act as a promoter of nucleation and crystal growth alone, in this study we show that proteolysis exerts an additional nucleation- and growth-promoting effect. Hydrolysis of full-length amelogenin by MMP-20 decreases the critical time needed for the protein and peptides to adhere and to cover the substrate. The formation and immobilization of a protein layer subsequently reduces the time for calcium phosphate crystallization. Coupling the proteolytic reaction to titration in the presence of 0.4 mg/ml rH174 has been shown to have the same effect on the crystal growth promotion as quadrupling the concentration of rH174 to 1.6 mg/ml. Controlling the rate and the extent of the proteolytic cleavage can thus be used to control the nucleation and growth rates in a protein-guided crystallization system.     

Hyrax application as a tooth-borne distractor for maxillary advancement

Distraction osteogenesis (DO) has become a mainstream surgical technique for patients with jaw deformities. The aim of this study was to report the use of internal DO in the treatment of maxillary hypoplasia in a patient with cleft lip and palate. The case illustrates a 17-year-old boy with class III malocclusion, maxillary deficiency, and cleft lip and palate. Because the patient was experiencing severe hypernasality, it was decided to treat him by DO. The treatment process began by mounting a hyrax in the upper jaw for lateral expansion. A second hyrax was mounted in a way to create anteroposterior expansion. One day after the second hyrax application, the patient underwent a modified Le Fort I osteotomy. He was instructed to turn the screws twice per day for 12 days. The treatment was continued by means of a conventional face mask for 2 months. After 16 months of active treatment, favorable correction of the skeletal problem was observed. The S-N-A angle increased by 5 degrees, and patient's hypernasality was comprehensively improved.     

Fracture toughness and hardness evaluation of three pressable all-ceramic dental materials

OBJECTIVES: This study evaluates the fracture toughness and hardness of three pressable all-ceramic materials: IPS-Empress, Empress 2 and an experimental ceramic material. METHODS: Fifteen discs and 15 bars per material were prepared. Fracture toughness was measured with two different techniques: indentation fracture and indentation strength. During the indentation fracture tests the hardness of each material was also measured. Statistical significance among groups of population was studied using one-way Anova and Tukey's multiple comparison tests. RESULTS: Fracture toughness results using the indentation strength technique (with three-point bending and biaxial flexure tests) were: IPS-Empress (1.39 (SD 0.3) and 1.32 (SD 0.3)); Empress 2 (3.14 (SD 0.5) and 2.50 (SD 0.3)) MPa x m(1/2); and the experimental ceramic (3.32 (SD 0.6) and 2.43 (SD 0.3)) MPa x m(1/2). The indentation fracture technique generated orthogonal cracks of different lengths for Empress 2 and the experimental ceramic, whether perpendicular or parallel to the lithium disilicate elongated crystals. Thus, two values were reported: Empress 2 (1.5 (SD 0.2) and 1.16 (SD 0.2)) MPa x am(1/2) and the experimental ceramic (1.67 (SD 0.3) and 1.15 (SD 0.15)) MPa x m(1/2). The IPS-Empress indentation fracture result was 1.26 (SD 0.1). The hardness results were: 6.6, 5.3 and 5.5 GPa for IPS-Empress, Empress 2 and the experimental ceramic, respectively. CONCLUSIONS: No significant differences in fracture toughness and hardness results were found between Empress 2 and the experimental ceramic (P>0.05 ANOVA). Both materials exhibited fracture toughness anisotropy following pressing. They demonstrated improved fracture toughness and reduced hardness compared with IPS-Empress P<0.05(ANOVA), which should be beneficial for clinical applications.     

Current status of predoctoral geriatric education in U.S. dental schools

The elderly constitute the fastest growing segment of the U.S. population. Dental schools must educate dental students so that they are competent and confident in managing the treatment needs of elderly patients. Programs in geriatric dentistry have been developed in response to the changing oral health needs of growing numbers of older adults. The purpose of this online survey was to identify the current status of predoctoral geriatric dental education in U.S. dental schools. A questionnaire relating to the teaching of geriatric dentistry was posted on the World Wide Web, and fifty-four US. dental schools were invited to complete the form. Data from completed questionnaires were submitted to the investigators via email. Following repeated phone calls and emails to urge school administrators to respond to the electronic questionnaire, a 100 percent response rate was achieved. All schools reported teaching at least some aspects of geriatric dentistry, and 98 percent had curricula that contain required didactic material. Sixty-seven percent of schools reported having a clinical component to geriatric dental teaching. Of these schools, the clinical content was required in 77 percent and elective in the rest. Thirty percent of schools reported a specific geriatric dentistry clinic within the school, and 11 percent had a remote clinical site. Sixty-three percent of schools have a geriatric program director or a chairman of a geriatric section. Over a third of schools indicated that they plan to extend the teaching of geriatric dentistry in the future. Geriatric dental education has continued to expand over the last twenty years and has established itself in the U.S. predoctoral dental curriculum. The format of teaching the subject varies considerably among the dental schools. Although didactic teaching of geriatric dentistry has increased markedly in the last two decades, clinical experience, both intramurally and extramurally, did not keep pace.     

The effect of thermocycling on the bonding of different restorative materials to access opening through porcelain fused to metal restorations

PURPOSE

Porcelain fused to metal (PFM) crowns provide the best treatment option for teeth that have a large or defective restoration. More than 20% of teeth with PFM crowns or bridges require non-surgical root canal treatment (NSRCT). This may be due to the effect of restorative procedures and the possible leakage of bacteria and or their by-products, which leads to the demise of the tooth pulp. Thus, this study was planned to compare the ability of the restorative materials to seal perforated PFM specimens.

MATERIALS AND METHODS

The study evaluates the ability of amalgam, composite or compomer restorative materials to close perforated PFM specimen''s in-vitro. Ninety PFM specimens were constructed using Ni-Cr alloys and feldspathic porcelain, and then they were divided into 3 groups: amalgam (A), composite + Exite adhesive bond (B) and compomer + Syntac adhesive bond (C). All the PFM samples were embedded in an acrylic block to provide complete sealing of the hole from the bottom side. After the aging period, each group was further divided into 3 equal subgroups according to the thermocycling period (one week for 70 cycles, one month for 300 cycles and three months for 900 cycles). Each subgroup was put into containers containing dye (Pelikan INK), one maintained at 5℃ and the other at 55℃, each cycle for 30 sec time. The data obtained was analyzed by SPSS, 2006 using one way ANOVA test and student t-test and significant difference level at (P<.01).

RESULTS

The depth of dye penetration was measured at the interfaces of PFM and filling materials using Co-ordinate Vernier Microscope. The lowest levels of the dye penetration for the three groups, as well as subgroups were during the first week. The values of dye leakage had significantly increased by time intervals in subgroups A and C.

CONCLUSION

It was seen that amalgam showed higher leakage than composite while compomer showed the lowest level of leakage.     

Culture of human gingival fibroblasts on a biodegradable scaffold and evaluation of its effect on attached gingiva: a randomized, controlled pilot study

BACKGROUND: An adequate width of attached gingiva is necessary to maintain healthy periodontium, especially in orthodontics or restorative treatments in periodontics. The purpose of this study was to evaluate the width of attached gingiva after clinical application of a cultured gingival graft compared to a periosteal fenestration technique. METHODS: This study was conducted on nine patients (18 sites) with insufficient attached gingiva adjacent to at least two teeth in contralateral quadrants of the same jaw. A small portion (approximately 3 x 2 x 1 mm) of attached gingiva (epithelial + connective tissue) was removed with a surgical blade. After culture of gingival fibroblasts, 2 x 10(5) cells in 250 microl nutritional medium were added to 250 microl collagen gel. One tooth in each patient was randomized to receive a periosteal fenestration technique for gingival augmentation (control) or a tissue-engineered mucosal graft (test). Clinical parameters measured at baseline and 3 months included width of keratinized tissue, probing depth, and width of attached gingiva. RESULTS: An increased amount of keratinized tissue was seen at all treated sites after 3 months. The mean increased amount of attached gingiva was 2.8 mm at test sites and 2 mm at control sites; this difference was significant (P < 0.05). CONCLUSION: Based on the results of this investigation, the tissue-engineered mucosal graft is safe and capable of generating keratinized tissue.     

Ewing sarcoma of the jaws

Three cases of Ewing sarcoma in the jaw bones are presented. The first patient is a 43-year-old woman with a rapidly growing tumor in the hard palate. The second patient is a 9-year-old girl with tumor in the left mandibular ramus and body. In both patients, the tumors were excised with significant safe margins. However, postoperative histopathologic evaluation revealed the presence of tumor cells in bony margins, necessitating a second surgery. The third patient is a 9-year-old boy with tumor in the right mandibular ramus and body. In patients 1 and 2, chemotherapy failed to control the tumor; however, in patient 3, chemotherapy resulted in significant shrinkage of the tumor and no further growth.     

A Longitudinal Survey for Genome-based Identification of SARS-CoV-2 in Sewage Water in Selected Lockdown Areas of Lahore City,Pakistan: A Potential Approach for Future Smart Lockdown Strategy

In 2019, the newly emerged SARS-CoV-2 virus caused pneumonia-like illness. The disease rapidly spread globally, leading to a worldwide outbreak referred to as the COVID-19 pandemic. The affected patients show symptoms of fever, dry cough, respiratory distress, myalgia, and gastrointestinal disturbance. As of April 5, 2021, 132,083,022 people worldwide were affected by COVID-19, while 2,868,454 people died due to the disease[1]. SARS-CoV-2-positive patients may remain asymptomatic or start showing symptoms in 2?14 days after exposure to the virus[2]. The viral infection can be diagnosed from nasopharyngeal, throat, alveolar lavage, lacrimal, blood, and stool samples. The patient starts shedding the virus in stool regardless of being symptomatic or asymptomatic, which makes sewage-based detection of the virus to be more beneficial in the early infection stage.