Stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional finite element analysis

Success/failure of dental implants depends on stress transfer and distribution at the bone-implant interface. This study aimed to assess the stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional (3D) finite element analysis (FEA). In this FEA, a geometric model of an edentulous maxilla, Zimmer screw-vent tantalum and solid titanium implants were modelled. Four models with the all-on-four concept were designed. The fifth model had 6 vertical implants (all-on-six). Two different implant types (porous tantalum and solid titanium) were modelled to yield a total of 10 models, and subjected to 200 N bilateral vertical load. Pattern of stress distribution and maximum von Mises stress values in cancellous and cortical bones around implants were analysed. In tantalum models, the effect of increasing the distal tilting of posterior implants was comparable to the effect of increasing the number of implants to 6 on von Mises stress values in cortical bone. However, in cancellous bone, the effect of increasing the tilting of posterior implants on stress was slightly greater than the effect of increasing the number of implants to 6. In solid titanium models, the effect of both of the abovementioned parameters was comparable on stress in cancellous bone; but in cortical bone, the effect of increasing the implant number was slightly greater on stress reduction. Despite similar pattern of stress distribution in bone around implants, higher maximum von Mises stress values around tantalum implants indicate higher stress transfer capacity of this type of implant to the adjacent bone, compared with solid titanium implants

Characteristics of anatomical landmarks in the mandibular interforaminal region : a cone-beam computed tomography study

Objectives: This study was conducted to assess appearance, visibility, location and course of anatomical landmarks in mandibular interforaminal region using cone-beam computed tomography (CBCT). Study design: A total of 96 CBCT examinations was re-evaluated to exploit anatomical landmarks. The examinations used the Promax 3D CBCT unit. A sole examiner carried out all the measurements. Visibilities of the anatomical landmarks were scored using a four-point rating scale. Results: The mandibular foramen, anterior loop, incisive canal and lingual foramen were observed in 100,84,83,49 % of the images, respectively. The mean size, diameter and width of anterior loop, incisive canal and lingual foramen were obtained 3.54± 1.41, 1.47±0.50 and 0.8 ± 0.09mm, respectively. Conclusion: It is not safe to recommend any definite distance mesially from the mental foramen. The diameter of the canals and foramens should be determined on a case-by-case basis to exploit the appropriate location for each individual

Determining the distance from the lingual frenum anterior attachment to the lower incisors’ incisal edges

Background. Occlusal rims are used to determine the jaw relationships in the transverse and vertical dimensions and estimate the inter-occlusal distance in edentulous patients. It is important to find ways to determine the height and shape of the occlusal rims correctly. This study was undertaken to determine the exact distance from the oral cavity floor to the incisal edges of mandibular incisors to serve as a guide for adjusting the height of the mandibular occlusal rim. Methods. Forty patients were selected and special trays were fabricated to prepare accurate stone casts on which the measurements were made at 0.01-mm accuracy. Two marks were placed on the casts at the incisal edges of mandibular incisors and at anterior attachment of lingual frenum. Then the distance between these two marks was determined on the vertical spindle of a surveyor using a digital Vernier measuring tool and recorded. Results. The results showed that the mean and standard deviation of the distances between the oral cavity floor and the incisal edges of lower incisors were 14.35 ± 1.68 mm, with a range of 10.2‒17.02 mm. The mean distances in males and females were 15.42 ± 0.97 and 13.28 ± 1.57 mm, respectively. T-test showed significant differences in this distance between males and females, with greater distances in males. Conclusion. The distance between the oral cavity floor and the incisal edges of mandibular incisors at anterior attachment of lingual frenum might be a proper criterion for the initial adjustment of occlusal rims

Prosthodontic rehabilitation of a bruxer patient with severely worn dentition: a clinical case report

The management of tooth wear has been a subject of increasing interest from both preventive and restorative points of view. This article describes the full mouth rehabilitation of a 54-year-old bruxer woman with a severely worn dentition and other dental problems including unsuitable restorations and several missing teeth. The treatment entailed using cast posts and cores, metal-ceramic restorations, and a removable partial denture. As with the treatment procedure of such cases, equal-intensity centric occlusal contacts on all teeth and an anterior guidance in harmony with functional jaw movements were especially taken into account

A Simple Method for Prosthodontic Rehabilitation of Edentulous Patient with Epidermolysis Bullosa: A Clinical Case Report

An abnormally small oral orifice is defined as microstomia. Microstomia may result from epidermolysis bullosa (EB), which consists of a group of disorders characterized by the presence of mechanical fragility of the skin with recurrent development of blisters and vesicles, resulting from minor mechanical friction or trauma. Since such patients have a small oral aperture, it may be impossible to take impression and fabricate dentures using conventional methods. In this article, a simple method for taking preliminary impressions from upper and lower edentulous ridges in one patient with limited mouth opening and then preparing the complete denture with custom denture teeth in a single unit was described

Effect of denture cleansing agents on tensile and shear bond strengths of soft liners to acrylic denture base

Background. The aim of the present study was to evaluate the effect of Corega and 2.5% sodium hypochlorite cleansing agents on the shear and tensile bond strengths of GC soft liner to denture base. Methods. A total of 144 samples (72 samples for tensile and 72 for shear bond strength evaluations) were prepared. The samples in each group were subdivided into three subgroups in terms of the cleansing agent used (2.5% sodium hypochlorite, Corega and distilled water [control group]). All the samples were stored in distilled water, during which each sample was immersed for 15 minutes daily in sodium hypochlorite or Corega solutions. After 20 days the tensile and shear bond strengths were determined using a universal testing machine. In addition, a stereomicroscope was used to evaluate fracture modes. Data were analyzed with one-way ANOVA, using SPSS 16. Results. The results of post hoc Tukey tests showed significant differences in the mean tensile and shear bond strength values between the sodium hypochlorite group with Corega and control groups (P=0.001 for comparison of tensile bond strengths between the sodium hypochlorite and control groups, and P<0.001 for the comparison of tensile bond strengths between the sodium hypochlorite and Corega groups and the shear bond strengths between the sodium hypochlorite and Corega groups, and sodium hypochlorite and control groups).The majority of failures were cohesive in the control and Corega groups and cohesive/adhesive in the sodium hypochlorite group. Conclusion. Immersion of soft liners in Corega will result in longevity of soft liners compared to immersion in sodium hypochlorite solution and sodium hypochlorite solution significantly decreased the tensile and shear bond strengths compared to the control and Corega groups

Effect of Different Disinfectants on Staphylococcus aureus and Candida albicans Transferred to Alginate and Polyvinylsiloxane Impression Materials

Background and aims. Several products have been marketed for disinfecting impression materials. The present study evaluated the effect of Deconex, Micro 10, Alprocid and Unisepta Plus sprays on Staphylococcus aureus and Candida albicans transferred to alginate and polyvinylsiloxane impression materials. Materials and methods. A total of 180 impressions of a maxillary model (90 alginate and 90 polyvinylsiloxane impressions) were taken for the purpose of this in vitro study. Half of the impressions were infected with Staphylococcus aureus and the other half were infected with Candida albicans. Then the microorganisms were cultured and their counts were determined. Subsequently, the impressions were divided into groups of 15 impressions each. Each group was disinfected with Deconex, Micro10, Alprocid and Unisepta Plus according to manufacturers' instructions except for the control group. The culturing procedure was repeated after disinfection and microbial counts were determined again. Data was analyzed by ANOVA and paired-sample t-test. Results. There were statistically significant differences in the means of S. aureus and C. albicans counts before and after the use of disinfectants (P < 0.05). The use of the four disinfectants reduced S. aureus counts to zero in 80% of the cases. There were no statistically significant differences in S. aureus count reductions between the four disinfectants evaluated (P = 0.31). Micro 10 was more effective on alginate; Deconex was more efficient for polyvinylsiloxane and Alprocid had a better efficacy in both impression materials in eliminating C. albicans (P < 0.05). Conclusion. All the disinfectants evaluated have high disinfecting postentials

Proportions of Maxillary Anterior Teeth Relative to Each Other and to Golden Standard in Tabriz Dental Faculty Students

Background and aims. Various methods are used to measure the size and form of the teeth, including the golden proportion, and the width-to-length ratio of central teeth, referred to as the golden standard. The aim of this study was to evaluate the occurrence of golden standard values and golden proportion in the anterior teeth. Materials and methods. Photographs of 100 dentistry students (50 males and 50 females) were taken under standard conditions. The visible widths and lengths of maxillary right and left incisors were calculated and the ratios were compared with golden standard. Data was analyzed using SPSS 14 software. Results. Review of the results of the means showed statistically significant differences between the width ratio of right lateral teeth to the central teeth width with golden proportion (P<0.001). Likewise, the difference was significant for the left side, too (P<0.001). Test results of mean differences showed that the mean difference between proportion of right laterals to centrals with golden proportion was significant (P<0.001). The difference was significant for the left side, too (P<0.001). As a result, there is no golden proportion among maxillary incisors. The review of results of mean differences for single samples showed that the mean differences between the proportion of width-to-length of left and right central teeth was statistically significant by golden standard (P<0.001). Therefore, considering the width-to-length proportion of maxillary central teeth, no golden standard exists. Conclusion. In the evaluation of the width-to-width and width-to-length proportions of maxillary incisors no golden proportions and standards were detected, respectively