Evaluation of stress distribution of porous tantalum and solid titanium implant-assisted overdenture in the mandible: A finite element study.

Aims: The present study aimed to evaluate the stress distribution of porous tantalum implant and titanium solid implant assisted overdenture (IAO) in mandibular bone by utilizing three-dimensional (3D) finite element (FE) analysis. Materials and Methods: In this FE study, an existing cone-beam volumetric tomography scan of a patient without any maxillofacial anomaly with an available acceptable IAO for mandible was used to attain the compartments of a completely edentulous mandible. Zimmer trabecular implants and locator attachment systems were selected as the case group (Model B), and Zimmer Screw-Vent implants and locator attachment system were chosen for the control (Model A), as overdenture attachments in the present study. The mandibular overdenture was scanned and digitized as a FE model. Two 3D FE models were designed as edentulous lower jaws, each with four implants in the anterior section of the mandible. Three forms of loads were directed to the IAO in each model: Vertical loads on the left first molar vertical molar (VM). Vertical loads on the lower incisors (VI). Inclined force buccolingually applied at left first molar (IM). Results: Under all loading conditions, the maximum strain values in peri-implant bone in Model A were less than Model B. Under VI, the greatest stress value around abutments in both models was about 2-3 times higher than the other loads. Under VM and IM loads, no significant difference was observed between models. Conclusion: Using trabecular metal implants instead of solid implants reduces strain values around both cortical and trabecular bone.

Comprehensive Treatments for Congenitally Missing Teeth and Generalized Diastema.

Congenitally missing teeth and/or hypodontia is a prevalent dental anomaly. There are different treatment options available for these conditions such as space maintenance, restoring the space by resin-bonded-fixed-partial-dentures (RBFPDs), and dental implants. This study addresses the comprehensive treatments for congenitally missing tooth and diastema using interdisciplinary approaches. One patient was treated with small-diameter-implants and the other one was treated using an intraoral scanner to make digital impression and fabricating RBFPDs with CAD/CAM system. Both patients were completely satisfied.

The effect of repeated torque tightening on total lengths of implant abutments in different internal implant‒abutment connections.

Background. Since the misfit of crown has an important role in clinical performance of implant-supported prostheses, and due to the impact of the settling effect on misfit, the aim of this study was to investigate the impact of torque forces on the total lengths of narrow and short implant abutments in different internal implant‒abutment connections. Methods. In four different implant‒abutment connections, 8 analog implants with a normal diameter (4 mm) and narrow abutment (4.5 mm) were selected from groups of internal hex, internal octagon, morse hex 6° and morse hex 11°. Each of them was mounted within plaster type IV, and 32 samples were obtained. Then, the amount of vertical displacement was measured by closing the impression copings and applying torques of 20 25 and 30 Ncm. This stage was repeated for the abutment. In the next stage, the resin pattern was built and measurements were performed after applying the torques mentioned. Finally, after making the frame, this stage was repeated, and the settling effect was statistically analyzed with ANOVA. Results. In the stages of impression coping, resin pattern and final prosthesis, HEXAGONE had significantly the highest and OCTAGONE had the lowest rates of settling, and the settling of morse hex 11° and 6° was between them. Conclusion. Octagon implant had significantly the lowest settling in various clinical and laboratory stages by applying different torques.

Effect of Non-surgical Periodontal Therapy on Serum and Salivary Concentrations of Visfatin in Patients with Chronic Periodontitis.

Background and aims. Visfatin, mainly secreted by visceral adipose tissue, especially by macrophages, plays an important role in regulating the defense and immune functions, and functions as a growth factor, a cytokine, an enzyme and more importantly as a proinflammatory mediator. The aim of the present study was to evaluate the effect of non-surgical periodontal treatment on serum and salivary levels of visfatin in patients with generalized moderate-to-severe chronic periodontitis. Materials and methods. Eighteen patients with generalized moderate-to-severe chronic periodontitis were selected based on periodontal parameters of gingival index (GI), probing pocket depth (PPD), clinical attachment level (CAL) and radiographic parameters. Serum and salivary samples were collected at baseline and one month following non-surgical periodontal therapy (scaling and root planing ([SRP]). Visfatin levels were measured using an ELISA kit. Data were analyzed by SPSS 15, using paired t-test and Pearson's correlation coefficient. Results. Mean salivary and serum levels of visfatin significantly decreased after non-surgical periodontal treatment (P<0.05). Changes in salivary visfatin levels were more prominent. Conclusion. According to the findings of this study it seems that there is a direct relationship between periodontal tissue inflammation and disease activity with salivary and serum visfatin levels.

The Comparison of Stress Distribution with Different Implant Numbers and Inclination Angles In All-on-four and Conventional Methods in Maxilla: A Finite Element Analysis.

Background and aims. All-on-four technique involves the use of tilted implants to allow for shorter cantilevers. This finite element analysis aimed at investigating the amount and distribution of stress in maxillary bone surrounding the implants with all-on-four vs. frequently used method with six implants technique using different numbers and inclination angles. Materials and methods. A 3D edentulous maxillary model was created and implants were virtually placed anterior to the maxillary sinus and splinted with a superstructure. In total, five models were designed. In the first to the fourth models, four implants were placed with distal implants inclined 0, 15, 30, and 45 degrees, respectively. In the fifth model, six vertical implants were placed. 100 N loading was placed in the left most distal region of the superstructure. Maximum von Mises stress values were evaluated in cancellous and cortical bone. Results. The maximum stress values recorded in cancellous and cortical bone were 7.15 MPa and 51.69 MPa, respectively (model I). The reduction in stress values in models II to V 6%, 18%, 54%, and 24% in cancellous bone and 12%, 36%,62%, and 62% in cortical bone, respectively. Conclusion. Increasing the inclination in posterior implants resulted in reduction of cantilever length and maximum stress decline in both cancellous and cortical bone. The effect of cantilever length seems to be a dominant factor which can diminish stress even with less number of implants.

Effect of Abutment Height on Retention of Single Cement-retained, Wide- and Narrow-platform Implant-supported Restorations.

BACKGROUND AND AIMS: In contrast to prepared natural dentin abutments,little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The aim of this study was to investigate the effect of im-plant abutment height on the retention of single castings cemented to wide and narrow platform implant abutments. MATERIALS AND METHODS: Thirty-six parallel-sided abutments (Biohorizon Straight Abutment) of narrow platform (NP) and wide platform (WP) sizes with their analogs were used. In each group of platform size, abutments were prepared with axial wall heights of 5, 4, 3, 2 mm (n=9). On the whole 72 castings were constructed, which incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond®. A uniaxial tensile force was applied to the crown using an Instron machine until cement failure occurred. Analysis of variance of the models were fit to determine the effect of height of abutment of the restorations on the mean tensile strength (α=0.05). RESULTS: The mean peak removal force for corresponding abutments was significantly different (P < 0.05): (1) with plat-form sizes: WP > NP; (2) with alteration of axial wall height for NP: 5 mm > 4 mm > 3 mm = 2 mm and for WP: 5 mm > 4 mm = 3 mm = 2 mm. CONCLUSION: The retention of NP cement-retained restorations is influenced by the wall height but not in same manner as WP. Restorations of narrow-platform size with longer abutment exhibited higher tensile resistance to dislodgement.

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 pro-portion, and the width-to-length ratio of central teeth, referred to as the golden standard. The aim of this study was to eval-uate 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.

The effect of disinfection by spray atomization on dimensional accuracy of condensation silicone impressions.

BACKGROUND AND AIMS: The condensation silicone impression materials are available, but there is little knowledge of their accuracy after disinfection. The objective of this study was to evaluate the effect of the disinfection by spray atomization on dimensional accuracy of condensation silicone impressions. MATERIALS AND METHODS: Impressions were made on a stainless steel master model containing a simulated two complete crown preparation with an edentulous space interposed using Spidex® and Rapid® impression materials. 44 impressions were made with each material, of which 16 were disinfected with 5.25% sodium hypochlorite, 16 were disinfected with 10% iodophor and 12 were not disinfected. Three dimensional measurements of working casts, including interpreparation distance, height, and diameter, were calculated using a measuring microscope graduated at 0.001 mm. Dimensional changes (mm) between the disinfected and non-disinfected working casts were compared. One-way analysis of variance (ANOVA) was employed to analyze the data (α=0.05). RESULTS: Disinfection of each condensation silicone material by spraying atomization with two different disinfectant material resulted in significant change in interpreparation distance (p<0.05). Changes in height and diameter were only significant in Spidex® impressions (p<0.05). CONCLUSION: Significant changes in the mean dimensions were seen as a result of disinfection by spraying; however, the dimensional changes do not seem great enough to cause critical positional distortion of teeth when fixed partial denture restorations are made.

A comparative study of the long term results of root coverage with connective tissue graft or enamel matrix protein: 24-month results

Background: The objective of this study was to compare the 24 month results of coronally advanced flap + enamel matrix derivates (EMD+CAF) and CAF+ connective tissue graft (CTG+CAF) in the treatment of Miller Class I recession defects.
Methods: Twelve patients with bilateral gingival recessions were treated with EMD+CAF or CTG+CAF. Vertical recession depth (VRD), keratinized tissue width (KTW), clinical attachment level (CAL), and clinical probing depth (CPD) were measured preoperatively, 1 and 2 years post surgery. A paired t-test and independent t-test were used to compare differences for the measured characters within and between groups, respectively. Results: After 24 months a significant decrease in VRD was observed in CAF + EMD (3.33±0.30 mm) and CAF + CTG (4.5 ± 0.28 mm) treated sites. There was also a significant increase in KTW (0.83±0.23 mm versus 2.08±0.14 mm in EMD+CAF and CTG+CAF sites, respectively). The gain in CAL was 3.54 ± 0.38 mm and 4.45±0.30 mm in EMD+CAF and CTG+CAF group, respectively. There were significant differences between the treatments for VRD, CAL, and KTW at the end of study. Conclusions: The CTG+CAF procedure seems to provide better long-term results than the EMD+CAF in obtaining root coverage, increasing the KTW and CAL gain (AU)

A comparative study of the long term results of root coverage with connective tissue graft or enamel matrix protein: 24-month results.

BACKGROUND: The objective of this study was to compare the 24 month results of coronally advanced flap + enamel matrix derivates (EMD+CAF) and CAF+ connective tissue graft (CTG+CAF) in the treatment of Miller Class I recession defects. METHODS: Twelve patients with bilateral gingival recessions were treated with EMD+CAF or CTG+CAF. Vertical recession depth (VRD), keratinized tissue width (KTW), clinical attachment level (CAL), and clinical probing depth (CPD) were measured preoperatively, 1 and 2 years post surgery. A paired t-test and independent t-test were used to compare differences for the measured characters within and between groups, respectively. RESULTS: After 24 months, a significant decrease in VRD was observed in CAF + EMD (3.33+/- 0.30 mm) and CAF + CTG (4.5 +/- 0.28 mm) treated sites. There was also a significant increase in KTW (0.83+/- 0.23 mm versus 2.08+/- 0.14 mm in EMD+CAF and CTG+CAF sites, respectively). The gain in CAL was 3.54 +/- 0.38 mm and 4.45+/- 0.30 mm in the EMD+CAF and CTG+CAF groups, respectively. There were significant differences between the treatments for VRD, CAL, and KTW at the end of study. CONCLUSIONS: The CTG+CAF procedure seems to provide better long-term results than the EMD+CAF in obtaining root coverage, increasing the KTW and CAL gain.

A Clinical Comparison of Cenobone (A Decalcified Freeze-dried Bone Allograft) with Autogenous Bone Graft in the Treatment of Two- and Three-wall Intrabony Periodontal Defects: A Human Study with Six-month Reentry.

BACKGROUND AND AIMS: Complete and predictable regeneration of tissue lost as a result of infection or trauma is the ultimate goal of periodontal therapy. Various graft materials have been successfully used in the treatment of intrabony defects. The purpose of this study was to evaluate the use of a decalcified freeze-dried bone allograft (Cerabone) with the autogenous bone graft as a gold standard in the treatment of human two- or three-wall intrabony periodontal defects. MATERIALS AND METHODS: This split-mouth study was done on 10 pairs of matched two- or three-wall intrabony periodontal defects with 5 mm or more probing depth and 3 mm or more depth of intrabony component following phase I therapy. In the control sites autogenous bone graft and in the test sites decalcified freeze-dried bone allograft were used. RESULTS: At baseline, no significant differences were found in terms of oral hygiene and defect charac-teristics. At six months, analysis showed a significant improvement in soft and hard tissue parameters for both treatment groups as compared to preoperative measurements. There were no statistical differ-ences in clinically-measured parameters between treatment groups after 6 months except for crestal resorption that increased significantly in control group (P = 0.25). Defect resolution and bone fill in the test and control groups were 2.5 ± 0.46 mm versus 2.7 ± 0.73 mm and 2 ± 0.62 mm versus 2.20 ± 0.52 mm, respectively. CONCLUSION: The results of this study demonstrated that both graft materials improved clinical parameters. The comparison of the two treatment groups did not show any significant differences in clinical parameters after six months. However, because of the limited amount of intra-oral donor bone, it is preferable to use decalcified freeze-dried bone allograft.