Stress Distribution in Bone and Implants in Mandibular 6-Implant-Supported Cantilevered Fixed Prosthesis: A 3D Finite Element Study.

PURPOSE: The purpose of the study was to evaluate by a 3-dimensional finite element analysis the load transmission to periimplant bone by a framework supported by 6 implants placed in an edentulous mandible and to compare the stress distribution for varying cantilever lengths. METHODOLOGY: A computerized model of the anterior segment of a mandible with a 6-implant-supported bridge was created in software. The length of the cantilever segment was considered as 10, 15, and 20 mm. A 150 N load was applied to the terminal point of the cantilever segment, and Von Mises stresses were analyzed along implants, framework, and bone. RESULTS: When the cantilever length was increased from 10 to 20 mm, the stress increased 79.66% in the framework, 68.16% in implants, and 59.96% and 52.81% in cortical and cancellous bones, respectively. CONCLUSION: The greatest amount of stress was seen around the distal-most region of the distal-most implant. The framework absorbed the maximum amount of stresses followed by the implants, cortical bone, and cancellous bone. Extension of the cantilever beyond 15 mm could lead to greater stress in the lingual cortical plate, which could compromise the integrity of the implants.

A Clinical Study Evaluating Changes in the Microbial Flora Around Dental Implants During Various Stages of Implant Restoration.

PURPOSE: This study evaluated the microbial colonization of dental implants in healthy patients before placing the implants and during the various stages of implant treatment. MATERIALS AND METHODS: Saliva (in completely edentulous patients) and gingival crevicular fluid samples (in partially edentulous patients) were collected from patients and analyzed to estimate the growth of microorganisms after culture. Samples were collected during 10 phases of implant placement and prosthesis insertion. Sixty dental implants, 18 of NobelReplace Select (Nobel Biocare) and 42 of GSIII/TSIII (Osstem), were evaluated. The microbial titer was estimated in colony-forming units (CFU) per milliliter. The percentage distribution of the organisms during the various phases was noted and the average was compared. RESULTS: Most prevalent microorganism found was gram-positive Streptococci (3.59 × 10 CFU/mL). The titer of Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, and Pseudomonas being 0.42 × 10 CFU/ml, 0.15 × 10 CFU/mL, 0.09 × 10 CFU/mL, and 0.03 × 10 CFU/mL, respectively. The titer of these organisms noted during the experimental phase was low. A similarity was observed in the maximum colony-forming unit per milliliter between baseline and completion of implant therapy indicating establishment of equilibrium. CONCLUSION: Regular microbial evaluation along with clinical and radiographic monitoring could help in recognizing the potential for periimplantitis and in prevention of the same.

The influence of thread geometry on biomechanical load transfer to bone: A finite element analysis comparing two implant thread designs.

BACKGROUND: The success of dental implants depends on the manner in which stresses are transferred to the surrounding bone. An important consideration is to design an implant with a geometry that will minimize the peak bone stresses caused by standard loading. The aim of this study was to assess the influence of implant thread geometry on biomechanical load transfer and to compare the difference between two different thread designs. MATERIALS AND METHODS: A three-dimensional finite element model of D2 bone representing mandibular premolar region was constructed. Two implants of differing thread geometries, 13-mm length, and 4-mm diameter along with superstructures were simulated. One design featured fourfold microthread of 0.4-mm pitch, 0.25-mm depth in the crestal one-third; 0.8-mm pitch, 0.5-mm depth in the apical two-third. The other design had a single-pitch microthread of 0.8-mm pitch, 0.25-mm depth in the crestal one-third; 0.8-mm pitch, 0.5-mm depth in the apical two-third. A static axial load of 100-N was applied to the occlusal surface of the prosthesis. ANSYS CLASSIC 9.0 (PA,USA)software was used for stress analysis as von Mises stresses. RESULTS: A comparison of von Mises stresses between two thread designs revealed that fourfold microthread allows better stress distribution within the implant body by 43.85%, abutment by 15.68%, its superstructure by 39.70% and 36.30% within cancellous bone as compared to single-pitch microthread. The effective stress transfer to the cortical bone is lowered by 60.47% with single-pitch microthread. CONCLUSION: Single-pitch microthread dissipates lesser stresses to cortical bone while the implant body, abutment, and superstructure absorb more stress. This will have a positive influence on the bone-implant contact and contribute to preservation of crestal bone. Implant with single pitch microthread will thus be preferable to be used in areas where the amount of cortical bone available is less.

Influence of platform switching on periimplant bone loss: a systematic review and meta-analysis.

PURPOSE: This meta-analysis aims to systematically review and draw a comparison between conventional implant designs and "platform-switched" implants in terms of crestal bone loss. MATERIALS AND METHODS: Electronic (PubMed) and hand searches were conducted. Literature, clinical studies, and case reports pertaining to reduction of crestal bone loss and obtaining better esthetic outcome by platform switching were reviewed till October 2011. Controlled trials comparing marginal bone-level changes around platform-switched and platform-matched implants were selected. For the assessment of accuracy, meta-analysis was performed. RESULTS: The marginal bone loss around platform-switched implants was significantly lesser than platform-matched implants (mean difference [MD]: -0.34; 95% confidence interval [CI]: -0.37 to -0.30; P < 0.00001). CONCLUSIONS: According to this review and meta-analysis, platform switching seems to preserve periimplant bone and soft tissue levels. However, long-term clinical studies on the proper diameter of abutment without deformation and the effective degree of platform switching in terms of the bone resorption are still awaited.

A correlation between bone (B), insertion torque (IT), and implant stability (S): BITS score.

STATEMENT OF PROBLEM: Although criteria for assessing bone quality have been reported, an overall score that correlates bone quality with the primary stability and secondary stability of implants is not yet available. PURPOSE: The purpose of this article was to propose a scoring index that will establish a correlation among the bone density values from computed tomography, maximum insertion torque values, and resonance frequency analysis in different phases of implant treatment. MATERIAL AND METHODS: In this study, 60 implant sites were evaluated to assess bone density (Hounsfield units), insertion torque values (Ncm), and primary stability and secondary stability (implant stability quotient values obtained by using resonance frequency analysis). On the basis of computed tomography data, the bone was classified as D1 to D4. The insertion torque was noted and classified into 2 groups, A and B. The implant stability quotient values obtained from resonance frequency analysis depicting primary stability and secondary stability were classified into 5 groups. The primary score noted was a result of the values obtained for the 3 parameters at the time of implant placement. The secondary score was obtained by considering the values of the bone density and resonance frequency analysis recorded at different time intervals. RESULTS: Bone densities of D2, D3, and D4 were noted, dividing the bone type into 3 groups. The maximum torque noted in the study was 40 Ncm. The difference between various insertion torque values and bone types was found to be statistically nonsignificant. Higher mean implant stability quotient values were obtained for primary and secondary stability for the D2 bone than for D3 and D4 bone. When analyzed according to the time of insertion, the mean values increased at second stage surgery in all bone types. The difference in mean values among all bone types was found to be statistically significant (P<.001). A comparison of primary and secondary implant stability quotient values in all bone types did not find any statistical significance (P=.780). A score was recorded at the time of implant placement and at the time of second stage surgery, and the prosthetic treatment was planned accordingly. CONCLUSIONS: The score highlights the importance of considering the association of bone quality, insertion torque values, and stability as denoted by implant stability quotient throughout treatment. Based on the variation in the score noted at recall visits, alterations in the treatment plan can be made with respect to the healing period and prosthetic design.

A survey on variability in shade selection by practicing dentists.

PURPOSE: To evaluate the variability in shade selection for general practitioners (GPs) and postgraduate (MDS) practitioners and to assess if a shade selection bias exists. MATERIALS AND METHODS: 2070 samples of the chosen shade(s) by 31 GPs and 18 MDS practitioners in the form of work authorization forms and slips were collected from dental laboratories. The mouth was divided into four quadrants: maxillary anteriors and posteriors, and mandibular anteriors and posteriors. The data was grouped and analyzed. RESULTS: The same shade or combination was repeated by the GPs and the MDS practitioners 38% and 35% of the time, respectively. The GP group prescribed a single shade in 84% of cases and a combination of two shades per tooth in 14% of cases, in contrast to the MDS practitioners, who prescribed a single shade in 51% of cases and two shades in 47% of cases. CONCLUSION: A shade selection bias exists among both general and MDS practitioners, as a particular shade or combination was repeated a significant number of times. However, MDS practitioners use a combination of two shades more frequently than general practitioners, who rely mostly on a single shade for a tooth.

Corrective primary impression technique.

The article describes a simple, quick and corrective technique for making the preliminary impression. It records the extensions better as compared to the impressions made using only impression compound. This technique is accurate and gives properly extended custom tray. Any deficiencies seen in the compound primary impression are corrected using this technique hence, this technique is called as a "corrective primary impression technique".