A 3-D finite element analysis of the effect of dental implant thread angle on stress distribution in the surrounding bone.

Background. This study aimed to evaluate the effect of an increase in fixture thread face angle on the amount and distribution of stresses in the surrounding bone of implants with four different thread shapes by three-dimensional finite element analysis. Methods. Eight different fixture designs, with v-shaped, buttress, reverse buttress, and trapezoid threads, and two face angles of 20 and 35 degrees, were modeled using a software program. Each model was affected by two static forces with different values and angles (200-N axial 0° force and 100-N 45° oblique force) to compare the distribution of stress in different fixture designs. Results. The maximum von Mises stress was detected in v-shaped threads. An increase in the angle of the threads to 35° significantly decreased maximum von Mises stress in cortical bone in v-shaped and reverse buttress threads; however, the von Mises stress in the trapezoid and buttress threads increased with an increase in the thread angle. Conclusion. Under the limitations of this study, although the shape of the thread and thread surface angle does not have a definite role in stress distribution in the bone surrounding the implant, they are effective in the amount and type of stress induced in the bone supporting the implant.

Effect of Beta-Blockers on Number of Osteoblasts and Osteoclasts in Alveolar Socket Following Tooth Extraction in Wistar Rats.

STATEMENT OF THE PROBLEM: Various researchers have suggested the use of ß2-adrenergic receptor antagonists in prevention or treatment of bone resorption. PURPOSE: This study aimed to evaluate the effect of ß2-adrenergic receptor antagonists on number of osteoclasts and osteoblasts involved in the healing of extraction socket of maxillary first molar in rats. MATERIALS AND METHOD: Maxillary first molars of 40 rats were extracted and divided into two groups. The test group received 0.1 mg/kg propranolol intraperitoneally daily. The controls received normal saline. At days 7, 14, 21 and 28 post-extraction, 5 rats were euthanized from each group. Maxillary bone was resected and the mean number of osteoblasts and osteoclasts in tooth socket was measured. RESULTS: After 1 week, the number of osteoclasts in the controls was significantly higher than the test group. A significant increase in the number of osteoclasts in both groups at week 1 was observed compared to the following weeks (p< 0.05). The number of osteoblasts in the controls at second week reached its maximum rate but stayed constant in the 3rd and 4th weeks. Osteoblasts in the test group increased similar to the controls but reached its maximum at 3rd week and showed a significant increase compared to the controls (p< 0.05). CONCLUSION: ß2 adrenergic receptor antagonists decrease the number of osteoclasts and increase the number of osteoblasts during extraction socket healing.

Finite Element Analysis of Soft-lined Mandibular Complete Denture and its Supporting Structures.

BACKGROUND AND AIMS: There are many edentulous people with severely resorbed residual ridges and non-resilient lin-ing mucosa that are unable to tolerate occlusal forces during functional and parafunctional movements. Lining the tissue surface of dentures with a flexible material can theoretically distribute and absorb forces with cushioning effect. The aim of this study was to evaluate the effect of a soft liner on stress levels in mandibular complete denture and its supporting struc-tures by finite element analysis. MATERIALS AND METHODS: A simplified 3-dimensional finite element model of relatively resorbed mandible, mucosa, denture and a soft liner was prepared. Then the model, with and without soft liner, underwent normal vertical and lateral occlusal forces. The stresses were analyzed using the ANSYS 12 software. RESULTS: Using the soft liner increased stress levels up to 18.5% and 30% in the cortical bone and mucosa, respectively, after vertical load was applied in the incisor region. Application of bilateral vertical load on the molar area increased stress in cortical bone u to 44% and in the mucosa up to 29%. Unilateral loading in the canine area increased stress level in the mucosa up to 63.5%. The highest stress was seen at denture base followed by the cortical bone. CONCLUSION: Use of soft liners increased stress in denture supporting structures. Higher level of stress concentration was observed primarily in the denture base followed by the cortical bone.

Frequency of Traumatic Ulcerations and Post-insertion Adjustment Recall Visits in Complete Denture Patients in an Iranian Faculty of Dentistry.

BACKGROUND AND AIMS: The first few days following the insertion of complete dentures are critical for the patients since they are struggling to adapt to their new dentures. This study aimed to evaluate the most common locations of traumatic ulcerations, their frequency and also the duration and number of adjustment visits required to achieve patient comfort fol-lowing placement of complete dentures. MATERIALS AND METHODS: Sixty patients were selected from edentulous patients referring to a removable prosthodontics department. Complete dentures were fabricated for the patients. After placement of dentures, all the patients were evaluated from the day after placement until patient comfort was achieved. Descriptive analysis was performed and chi-squared test was used to evaluate the associations between lesions, post-insertion visits and gender. RESULTS: A total of 85.8% of patients required denture adjustment because of mucosal injuries during their first visit fol-lowing denture placement. Maxillary and mandibular dentures did not require further adjustments after fourth and sixth visits, respectively. No significant differences were detected between males and females in the number of mucosal injuries in the anatomical areas evaluated in the maxilla and mandible using Fisher's exact test (P > 0.05). Furthermore, the number of mandibular dentures requiring adjustments was significantly higher than maxillary dentures in all the post-insertion ap-pointments (P < 0.001). CONCLUSION: Since most mucosal injuries are located in the vestibule, adequate extension of denture flanges, especially during border molding, and use of pressure indicators that reveal over-extended borders, play an important role in decreas-ing mucosal injuries and improving patient comfort following complete denture placement.

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 de-velopment 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.

Comparison of the Effect of Mouthwashes with and without Zinc and Fluocinolone on the Healing Process of Erosive Oral Lichen Planus.

BACKGROUND AND AIMS: Lichen planus is a chronic inflammatory disorder with unspecified etiology, appearing as a result of stress, genetic predisposition and immunologic factors. Erosive type of the disease is more important because of its clinical symptoms of pain, irritation and malignancy risk. Despite various medications used, a definite cure for lichen planus is un-known. Regarding the effect of zinc on healing of ulcers, the aim of this study was to compare the effect of a mouthwash with and without zinc and fluocinolone on healing of erosive oral lichen planus. MATERIALS AND METHODS: Twenty randomly-selected patients with erosive oral lichen planus were divided into two groups of 10. One group received zinc mouthwash with fluocinolone ointment and the other group received placebo with ointment. The largest dimension of the ulcers was measured by digital calipers and the intensity of pain was determined by visual ana-logue scale. Data was analyzed with Mann-Whitney U test. RESULTS: Pain, irritation and lesion surface area decreased in both groups. Decrease in pain severity was identical in both groups (P = 0.11). However, decrease in surface area with zinc mouthwash plus fluocinolone was more than that with only fluocinolone (P = 0.037). CONCLUSION: 0.2% zinc mouthwash plus fluocinolone and only fluocinolone were both effective in decreasing pain, irrita-tion, and surface area of OLP. However, decrease in surface area with zinc mouthwash plus fluocinolone was more than that with fluocinolone alone.

A study of parallelism of the occlusal plane and ala-tragus line.

BACKGROUND AND AIMS: Orientation of the occlusal plane is one of the most important clinical procedures in prostho-dontic rehabilitation of edentulous patients. The aim of this study was to define the best posterior reference point of ala-tragus line for orientation of occlusal plane for complete denture fabrication. MATERIALS AND METHODS: Fifty-three dental students (27 females and 26 males) with complete natural dentition and Angel's Class I occlusal relationship were selected. The subjects were photographed in natural head position while clenching on a Fox plane. After tracing the photographs, the angles between the following lines were measured: the occlusal plane (Fox plane) and the superior border of ala-tragus, the occlusal plane (Fox plane) and the middle of ala-tragus as well as the occlusal plane (Fox plane) and the inferior border of ala-tragus. Descriptive statistics, one sample t-test and independent t-test were used. P value less than 0.05 was considered significant. RESULTS: There was no parallelism between the occlusal plane and ala-tragus line with three different posterior ends and one sample t-test showed that the angles between them were significantly different from zero (p<0.05). However, the supe-rior border of ala-tragus line had the lowest mean angle, 1.80° (3.12) and was almost parallel to the occlusal plane. CONCLUSION: The superior border of the tragus is suggested as the posterior reference for ala-tragus line.

Pattern of occlusal contacts in eccentric mandibular positions in dental students.

BACKGROUND AND AIMS: This study observed occlusal contacts and their area on the teeth during lateral mandibular movements. The percentage of each occlusal pattern was determined. MATERIALS AND METHODS: FIFTY SUBJECTS (MALE: 27, female: 23), aged 20-29 years, were included in the study. The criteria for selection were as follow: all subjects (i) were in their twenties; (ii) had normal occlusal alignment, no temporomandibular signs and symptoms with Angle's Class I relationship; (iii) had full dentition except for third molars; (iv) had no history of orthodontic therapy; and (v) had no restorations involving a cusp. The occlusal contacts were recorded with occlusion foil in three lateral excursions: 1, 2 and 3 mm from the maximum intercuspation. Data were analyzed with chi-square test. RESULTS: Most of working-side contact patterns were classified as group function (60%). Canine protection was rare (17%). Contact patterns other than canine protection and group function were found in 23% of the contact patterns on the right side. On the left side, group function was seen in 51%, canine protection in 21% and others patterns in 28% of the studied subjects. CONCLUSION: On laterotrusion, most subjects had group function on the working side but canine protection was rare.

Fluoxetine enhances cutaneous wound healing in chronically stressed Wistar rats.

OBJECTIVES: To evaluate the histologic and clinical effects of fluoxetine administration on wound healing in chronically stressed and nonstressed Wistar rats. STUDY DESIGN: Full-thickness incisional wounds were created on the lower back of 72 female Wistar rats. Animals were divided into 2 stress and nonstress groups according to application of stress regimen and 3 subdivisions based on placebo, acute, or chronic administration of fluoxetine. Wound length, width, and linear healing rate based on wound area were measured for 2 weeks postwounding. Biopsies of 3 rats from each group were taken at days 1, 4, 7, and 14 to perform histomorphometric measurements by light microscopy. Analysis of covariance and analysis of variance were used to analyze wound length and other variables, respectively. RESULTS: Fluoxetine treatment significantly reduced mean wound length and healing period (P<.01). Although stress decreased the linear healing rate by 48%, fluoxetine treatment increased it by 68% and 31% in stressed and nonstressed rats, respectively. Stress significantly diminished infiltration of neutrophils and monocytes (P<.01), disrupted spatial organization of fibroblasts, and delayed neovascularization. Fluoxetine precluded these effects successfully. CONCLUSION: Fluoxetine significantly improves healing of cutaneous wounds in stressed and, to a lesser extent, in nonstressed animals.