Dental Research Journal
Volume:19 Issue: 4, Apr 2022

Masking dark tooth structure or darkness of oral cavity with ceramic restorations is an important concern. The aim of this study was to determine the minimum thickness of a multilayer all‑ceramic restoration (IPS‑emax Press) required for a proper masking in these situations.

In this experimental in vitro study, 36 multilayer ceramic disks of IPS e.max Press (IvoclarVivadent, Schaan, Liechtenstein) with the diameter of 13 mm were prepared and allocated in six groups of different core/veneer thicknesses: 0.4/0.4 mm (G1), 0.5/0.5 mm (G2), 0.6/0.6 mm (G3), 0.8/0.7 mm (G4), 1.0/0.8 mm (G5), and 1.1/0.9 mm (G6). For backgrounds, the standard black tile of spectrophotometer (B) was used to stimulate the darkness of oral cavity, and an opaque ceramic (OC) of IPS‑emax Press (OC) was fabricated to determine the masking ability. CIELAB values of all disks on B and OC backgrounds were measured, and ΔE was calculated between two backings. One‑way ANOVA and post hoc tukey test were used to analyze the data. ΔE ≤3.3 and P < 0.05 were considered, respectively, as the clinically acceptable limit and the level of statistical significancy.

The mean ΔE between B and OC of groups 4 (2.83 ± 0.80) and 5 (1.46 ± 0.36) were within the range of the clinically acceptable color difference (ΔE ≤3.3); thus these groups could properly mask the black background. A trend was existed in the results as by increasing the thickness, ΔE was decreased.

A thickness of 1.5 mm of a multilayer ceramic restoration (IPS e.max Press) is required to mask a dark discoloration.

Considering the studies on the effects of bleaching materials on properties of dental materials, The aims of this in vitro study were to evaluate the effects of two different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC.

In this experimental in vitro study, 30 rectangular‑shaped specimens(2 mm width × 2 mm height × 12 mm length) for flexural strength and 30 specimens (5 mm width × 5 mm length × 2 mm height) for microhardness tests were prepared from VITA ENAMIC blocks 12 × 14 × 18 mm. The specimens were polished using silicon‑carbide sandpapers 400, 600, 800, 1200, 2000 under flow of water for 60 s each. The prepared samples for flexural strength and microhardness were divided into 3 subgroups (n = 10): control group (C), samples bleached using Opalescence PF 15% (B15), and samples bleached with Opalescence Xtra Boost 40% (B40). Flexural strength measurement was done using a universal testing machine, and microhardness test was done using Vickers. Data were analyzed using analysis of variance and post hoc tests and P < 0.05 was considered significant.

The mean microhardness values of C, B15, and B40 groups were 255.46 ± 3.02, 249.86 ± 4.18, and 235.53 ± 4.61 kgf/mm2 . Opalescence PF 15% and Opalescence Xtra Boost 40% affected microhardness of ENAMIC significantly (P < 0.05). The mean flexural strength values of C, B15, and B40 groups were 155.26 ± 16.13, 142.14 ± 11.52, and 133.39 ± 16.13 MPa. A significant decrease in flexural strength was found between the C and B40 groups (P = 0.007). However, the difference between flexural strength of the C and B15 groups was not significant (P > 0.05).

Our study showed that both concentrations of bleaching agents can affect microhardness of ENAMIC. Moreover, hydrogen peroxide 40% has a negative effect on the flexural strength of ENAMIC

The mechanical and thermal properties of polymethyl methacrylate, as the most commonly used material for the fabrication of dental prostheses, should be improved due to its structural weaknesses. The present study aimed to compare the flexural strength and thermal conduction of two heat‑cured and self‑cured acrylic resins reinforced with aluminum oxide nanoparticles.

In this in vitro study, a total of 114 samples consisting of heat‑ and self‑cured three subgroups (1% and 3% Al2 O3 and the control) with 66 samples for the thermal conduction (n = 11) and 48 samples for the flexural strength (n = 8) tests were prepared. Flexural strength was assessed with a three‑point bending test using a universal testing machine. One‑way ANOVA was applied for data analysis, followed by post hoc Tukey paired group comparison tests (P < 0.05).

An increase in the aluminum oxide nanoparticle percentage in acrylic resins increased the thermal conduction in heat‑cured acrylic resin from 2.142 ± 0.0298 to 2.487 ± 0.0359 m (2)/sec and in self‑cured acrylic resin from 2.0150 ± 0.02646 to 2.1475 ± 0.04031 m (2)/sec and decreased the flexural strength in heat‑cured acrylic resin from 60.521 ± 8.9278 to 49.747 ± 4.4729 MPa and in self‑cured acrylic resin from 37.573 ± 10.9237 to 35.569 ± 6.1531 MPa (P < 0.05).

The incorporation of aluminum oxide nanoparticles adversely affected acrylic resin flexural strength; however, it increased the thermal conduction

In Iran, the inequitable distribution of health‑care staff, especially dental practitioners between rural and urban areas has a major impact on the delivery of care for those living in rural communities. This study investigated the factors affecting the retention of dental practitioners to stay in the rural areas.

This is a cross‑sectional study conducted in 2019. All dental practitioners working in health services centers covering a population lower than 20,000 people in Kerman province participated in this study (n = 81). A researcher‑designed questionnaire was used for the data collection. The data were analyzed using the descriptive statistics and logistic regression through the SPSS software.

The mean age of the participants was 29.2 ± 6.5 and 39.5% were female. The results showed that about two‑thirds of native dentists (with local origin), 73.3% of married dentists, and all dental practitioners who had no children or had a child under the age of six were willing to continue working with their current Comprehensive centers of health services compared to other dentists. Univariate and multivariate logistic regression showed that there was a significant relationship among dentists’ age, monthly salary, and facilities available in the area (place of residence, availability of vehicles, etc.), view of dental practitioners on living in a rural area, and view of dentists’ families on living and working in the area (p ˂ 0.05).

More than half of the dental practitioners declared their willingness to stay in rural areas, although, in practice, this amount of presence in rural areas does not meet the needs of residents. Financial issues, amenities, and facilities in the rural areas can have a positive impact on the retention of dental practitioners.

Accurate shade matching of metal‑ceramic restorations with natural teeth is one of the most challenging aspects of dental restorations and esthetic dentistry. The aim of this study was to evaluate of the color parameters of two types of porcelain systems VMK Master and VM13 porcelain with VITA 3D‑master shade guide.

In this in vitro study a total of 56 metal discs (10 mm diameter and 2 mm thickness) were fabricated. Each of the disks was veneered with porcelain (Vita Zahnfabrik, Bad Sackingen, Germany) of the VITA shade. The discs were randomly divided into four groups (2M2 and 3M2 from VM13, 2M2 and 3M2 from VMK master) of 14 (n = 14). The spectrophotometer was used for taking color measurements based on the numerical color data of the CIELAB color system. Data analysis was performed by t‑test (P < 0.05).

Comparison of color parameters in different porcelain showed that the type of porcelain caused a significant difference in color parameters (L, a, and b) (P < 0.05). The degree of translucency (L*) or glaze of VMK porcelains was higher than VM13, but the parameters a* and b* were higher in VM13 porcelains than VMK (P < 0.05). Furthermore, the color difference of two porcelain in 2M2 (1.63 ± 0.84) and 3M2 (1.71 ± 0.96) shades was within the acceptable clinical limit. Considering the total color difference (ΔE), there were no significant differences between the ΔE values produced by any of shades (P > 0.05).

In the present study, the spectrophotometric analysis revealed that the porcelain shade type causes a change in the color parameters, but the color difference between two porcelains VMK and VM13 is within the acceptable range of clinical color. Therefore, both porcelain systems with 2M2 and 3M2 shades are suitable for enhancing the results of restorative dentistry

The reduction of Streptococcus mutans from the oral cavity or its adherence to tooth surfaces can prevent or decrease the progression of caries. In this study, the antimicrobial and anti‑adherence properties of Pistacia atlantica (P. atlantica) resin (Essential oil [EO] and methanolic extract [ME]) were investigated on S. mutans strains.

In this in vitro experimental study, the growth rate, biofilm formation ability, and antibiotic susceptibility profile of S. mutans ATCC35668 and 3 strains isolated from caries lesions were studied. The EO and ME of P. atlantica resin were prepared. The anti‑bacterial and anti‑adherence properties of them were evaluated using microdilution and microplate adherence tests, respectively. The data were statistically analyzed using SPSS with one‑way and two‑way analysis variance. Direct comparisons between the groups were made using the Wilcoxon W‑Mann–Whitney U‑test. Statistical significance was set at P < 0.05.

All target strains showed the same growth rate and antibiotic susceptibility profile and were found strongly adherent. Both EO and ME showed moderate anti‑bacterial properties (growth reduction up to 47.1% and 39.1%, respectively) against S. mutans, while the anti‑bacterial effect of EO was higher than ME, significantly (P < 0.05). In all tested concentrations, EO showed a significantly stronger anti‑adherence activity (50%–80%) than ME.

The results showed an anti‑cariogenic effect of EO extracted from P. Atlantica resin. Considering that S. mutans adhesion is a necessary step in the beginning and progression of dental caries, this study can suggest the use of such extract in mouthwashes or toothpaste as an alternative agent for preventing bacterial attachment and biofilm formation.

Dental implants are known as a widely accepted and predictable method to replace missing teeth. Many factors, including using a class of drugs, such as β‑blockers, can improve the osseointegration of dental implants. This study aimed to investigate the relationship between administrating propranolol and osseointegration in dental implants.

This experimental animal study was performed on four native male street dogs of 11–13 kg of weight and 16–20 months of age. The specimens underwent teeth extraction. After that, the dogs were randomly divided into two groups. The first group contains two control dogs which would receive oral saline. The second contains two dogs which would receive oral tablets of propranolol daily. After a period of healing, three titanium implants were inserted in each of speciments’ left mandibular quadrant, and treatment was resumed with propranolol and saline administration in case and control group, respectively. After 4 weeks, one of control group dogs and one of case group were anesthetized, and dental implants were removed alongside the peripheral bone marrow using a trephine drill. Meanwhile, the other two dogs (1 control and 1 propranolol administered dogs) were anesthetized after 9 weeks of implant placement, and the same procedure was carried out.

Due to the histomorphometric assessment, the mean score of bone implant contact (BIC) in week 4 was significantly higher in case group compared to control one (68.33% vs. 20.22%). In week 9, the mean BIC score was higher in case group compared to control group (68.60% vs. 50.17%); meanwhile, in contrast to week 4, it was not statistically significant. In both case and control groups, the formation of woven and lamellar bone was more significant in week 4 rather than week 9.

Administration of systemic β‑blockers can improve dental implants osseointegration process

Crouzon syndrome is an autosomal dominant trait, leading to midface deficiency, undeveloped orbits, short nasal dorsum, and exophthalmos as the typical clinical features. Early correction of craniofacial problems can improve patients’ quality of life, but many of these patients with Crouzon syndrome are seeking treatment in older ages when they are missed for multidisciplinary management and distraction technique in proper timing. Modified LeFort III osteotomy is one of the treatment options that can be used for proper resolution in adult patients. The present case report study aims to describe a patient with midface deficiency due to the Crouzon syndrome who has undergone a combination of modified LeFort III osteotomy with the periocular approach and LeFort I osteotomy, nasal dorsum augmentation accompanied by genioplasty, wholly as a single surgical procedure which has been shown that can result in highly satisfactory outcomes for both patient and surgeon.

MicroRNAs are a class of small noncoding ribonucleic acids that perform a critical role in adjustment of gene expression. miRNAs‑155 (miR‑155) participates in controlling inflammation. Periodontitis is defined as inflammatory disorder of tissues surrounding the teeth. In this study, the expression levels of miR‑155 and its target genes, tumor necrotizing factor alpha (TNF‑α), and interleukin‑6 (IL‑6) were evaluated in a group of Iranian patients.

This sectional study was performed on 10 healthy controls and 10 individuals with chronic periodontitis by means of polymerase chain reaction (PCR) test. For each individual, clinical parameters including probing depth and clinical attachment loss and blood samples were measured. Levels of miR‑155, TNF‑α, and IL‑6 were quantified using real‑time PCR (α=0/05) and the results were analyzed by Mann–Whitney U test.

The level of miR‑155 was significantly higher in patients with chronic periodontitis(P < 0.001). A positive correlation was observed between the level of miR‑155 and clinical parameters(P < 0.05). Level of miR‑155 in tissue samples was correlated with blood samples although the expression level was higher in blood samples.

As the expression level of miR‑155, TNF‑α, and IL‑6 genes was higher in subjects with chronic periodontitis than healthy individuals, it might suggest a role for miR‑155 in patients with chronic periodontitis.

This study clinically and histologically compared the human pulp response to direct pulp capping (DPC) with mineral trioxide aggregate (MTA), Biodentine, and propolis in 2 months.

In this clinical trial evaluated 41 premolars candidate for extraction due to orthodontic purposes of patients between 15 and 25 years of age. A group of 5 was separated randomly as the negative control. The remaining teeth were randomly divided into three experimental groups of 12 after mechanical exposure of the pulp by bur in high‑speed handpiece under air and water spray. The exposed areas were capped with MTA, Biodentine, or propolis. Glass ionomer was applied as base over the cap. The teeth were restored with composite resin. Patients were recalled in 2 months for clinical and radiographic examinations and also pulp vitality test. Teeth were then extracted. Slides were prepared and tissue sections were evaluated for the presence and severity of inflammation, dentinal bridge, and continuity. Data were analyzed using the Chi‑square and Fisher’s exact tests.

The clinical success rate was 100% in the MTA and 91.7% in both the propolis and Biodentine groups. The presence and severity of pulpal inflammation and dentinal bridge formation were similar in all the experimental groups (P > 0.05). Dentinal bridge formation was similar in the MTA and Biodentine groups and was higher than in the propolis group. Continuation of dentinal bridge in the MTA group was significantly higher than that in the Biodentine and propolis groups (P < 0.05).

MTA, Biodentine, and propolis are equally effective for DPC