ABSTRACT
PURPOSE: The purpose of this study is to compare the effect of implant-abutment connections, abutment angulations, and screw lengths on screw loosening (SL) of preloaded abutment using three dimensional (3D) finite element analysis. MATERIALS AND METHODS: 3D models of implants (conical connection with hex/trilobed connections), abutments (straight/angulated), abutment screws (short/long), and crown and bone were designed using software Parametric Technology Corporation Creo and assembled to form 8 simulations. After discretization, the contact stresses developed for 150 N vertical and 100 N oblique load applications were analyzed, using ABAQUS. By assessing damage initiation and shortest fatigue load on screw threads, the SL for 2.5, 5, and 10 lakh cyclic loads were estimated, using fe-safe program. The obtained values were compared for influence of connection design, abutment angulation, and screw length. RESULTS: In straight abutment models, conical connection showed more damage (14.3%-72.3%) when compared to trilobe (10.1%-65.73%) at 2.5, 5, and 10 lakh cycles for both vertical and oblique loads, whereas in angulated abutments, trilobe (16.1%-76.9%) demonstrated more damage compared to conical (13.5%-70%). Irrespective of the connection type and abutment angulation, short screws showed more percentage of damage compared to long screws. CONCLUSIONS: The present study suggests selecting appropriate implant-abutment connection based on the abutment angulation, as well as preferring long screws with more number of threads for effective preload retention by the screws.
ABSTRACT
PURPOSE: To hypothesize a new theory based on soft tissue reference points on lateral profile photographs (LPPs) for determining the vertical dimension of occlusion (VDO), as there is need to explore for simple strategies. MATERIALS AND METHODS: Fifty-three participants in the age range of 20-27 years who met the inclusion criteria were recruited. LPPs were taken for all participants using standard protocol and duplicate copies obtained, on which five soft tissue reference points, nasion (Stn), subnasale (Stsn), porion (Stp), gnathion (Stgn), and gonion (Stg) (Stg prenoted on the face) were marked and joined to form angles; distance between Stsn and Stgn was considered as VDO in LPP (VDO-LP). The angle formed between Stn-Stsn-Stgn and Stn-Stsn-Stg; Stp-Stg-Stgn and Stp-Stg-Stsn was correlated; two simple linear regression models were developed to predict Stn-Stsn-Stgn and Stp-Stg-Stgn using Stn-Stsn-Stg and Stp-Stg-Stsn as independent variables. Using the formulae, VDO-LP predicted was constructed and correlated with the actual values. RESULTS: The angle Stn-Stsn-Stgn had a statistically significant moderate positive correlation with Stn-Stsn-Stg (r = 0.57, P < 0.001) and angle Stp-Stg-Stgn, a significant strong positive correlation with Stp-Stg-Stsn (r = 0.81, P < 0.001). Using simple linear regression analysis, the following formulae were obtained: Stn-Stsn-Stgn (in degrees) = 0.776 Stn-Stsn-Stg (in degrees) +79.01 and Stp-Stg-Stgn (in degrees) =1.331 Stp-Stg-Stsn (in degrees) +10.2. The predicted and actual VDO-LP values were in strong positive correlation with a coefficient of 0.8. CONCLUSION: With the use of simple landmarks on LPP, it is possible to reconstruct the lost facial dimensions during prosthetic replacement of lost teeth.
ABSTRACT
STATEMENT OF PROBLEM: Many methods are reported in literature to determine freeway space (FWS), but they yield dissimilar measurements. PURPOSE: Recording FWS of patients during prosthetic rehabilitation is one of the important steps in dentistry. The purpose of this study is to evaluate the ability to predict FWS using lateral profile photographs (LPPs) in edentulous participants. MATERIALS AND METHODS: Fifty-three participants in the age range of 20-27 years who met the inclusion criteria were recruited. LPP were taken for all participants using standard protocol and duplicate copy obtained; on which three soft tissue reference points, porion (Stp), gnathion (Stgn), and gonion (Stg) (Stg prenoted on the face) were marked and joined to form an angle Stp-Stg-Stgn. This angle was correlated with the mean FWS obtained using 3 methods, swallowing, phonetics, and no command. Simple linear regression model was used to develop a prediction formula for FWS using Stp-Stg-Stgn angle as the independent variable. RESULTS: The angle Stp-Stg-Stgn had a significant negative correlation with FWS (r = -0.76, P < 0.001). Using simple linear regression analysis, the following formula was obtained: FWS (in millimeters) = 11.405 - 0.072 × (Stp-Stg-Stgn angle in degrees). CONCLUSION: Within the limitations of this study, considering the usage of LPP as a method to determine the FWS can be recommended.
