Evaluation of reliability of zirconia materials to be used in implant-retained restoration on the atrophic bone of the posterior maxilla: A finite element study.

PURPOSE: Zirconia materials have been used for implant-retained restorations, but the stress distribution of zirconia is not entirely clear. The aim of this study is to evaluate the stress distribution and risky areas caused by the different design of zirconia restorations on the atrophic bone of the posterior maxilla. MATERIALS AND METHODS: An edentulous D4-type bone model was prepared from radiography of an atrophic posterior maxilla. Monolithic zirconia and zirconia-fused porcelain implant-retained restorations were designed as splinted or non-splinted. 300-N occlusal forces were applied obliquely. Stress analyses were performed using a 3D FEA program. RESULTS: According to stress analysis, the bone between the 1) molar implant and the 2) premolar in the non-splinted monolithic zirconia restoration model was stated as the riskiest area. Similarly, the maximum von Mises stress value was detected on the bone of the non-splinted monolithic zirconia models. CONCLUSION: Splinting of implant-retained restorations can be more critical for monolithic zirconia than zirconia fused to porcelain for the longevity of the bone.

The size of the esophageal hiatus in gastroesophageal reflux pathophysiology: outcome of intraoperative measurements.

OBJECTIVE: The aim of the study was to investigate the impact of the size of the esophageal hiatus on lower esophageal sphincter pressure (LESP) and acid reflux. METHODS: Patients with gastroesophageal reflux disease who underwent Nissen fundoplication in 2006-2008 were included. All underwent esophageal manometry and 22 had 24-h pH monitoring. The area of the esophageal hiatus was calculated from a photograph shot during surgery. A hiatal index was calculated via division of hiatal area with body mass index (BMI). Correlation and logistic regression analysis were performed. RESULTS: Twenty-eight patients (average age 44, 14 males) were enrolled. The mean BMI, LESP, DeMeester score, hiatal area, and hiatal index were 27 +/- 3.9 kg/m(2), 11.7 +/- 6.6 mmHg, 43 +/- 34, 3.83 +/- 1.24 cm(2), and 0.143 +/- 0.048, respectively. There was a significant negative correlation between hiatal area, hiatal index and LESP (-0.513, p = 0.005, r = -0.439, p = 0.019 respectively). Additionally there was a negative correlation between hiatal area and total LES length (r = -0.508, p = 0.013) and a significant positive correlation between hiatal area, hiatal index, and DeMeester scores (0.452, p = 0.035, 0.537, p = 0.01, respectively). Height and hiatal area were significant factors in multiple linear regression. CONCLUSIONS: The size of the esophageal hiatus significantly affects LESP and acid reflux, and hiatal index is a new value, which appears to reflect the amount of acid reflux. Total LES length is also shortened in patients with a large hiatus.

Influence of occlusal forces on stress distribution in preloaded dental implant screws.

STATEMENT OF PROBLEM: Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. PURPOSE: The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. MATERIAL AND METHODS: Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. RESULTS: Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite element models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. CONCLUSION: Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.