Zygomatic implants: the impact of zygoma bone support on biomechanics.

Maxillectomy and severely resorbed maxilla are challenging to restore with provision of removable prostheses. Dental implants are essential to restore esthetics and function and subsequently quality of life in such group of patients. Zygomatic implants reduce the complications associated with bone grafting procedures and simplify the rehabilitation of atrophic maxilla and maxillectomy. The purpose of this study was to compare, by means of 3-dimensional finite element analysis, the impact of different zygomatic bone support (10, 15, and 20 mm) on the biomechanics of zygomatic implants. Results indicated that maximum stresses within the fixture were increased by 3 times when bone support decreased from 20 to 10 mm and were concentrated at the fixture/bone interface. However, stresses within the abutment screw and the abutment itself were not significantly different regardless of the bone support level. Supporting bone at 10 mm sustained double the stresses of 15 and 20 mm. Fixture's deflection was decreased by 2 to 3 times when bone support level increased to 15 mm and 20 mm, respectively. It was concluded that zygomatic bone support should not be less than 15 mm, and abutment screw is not at risk of fracture regardless of the zygomatic bone support.

Marginal bone loss influence on the biomechanics of single implant crowns.

Marginal bone loss, whether it is physiological or pathological, is one of the implant treatment complications. The biomechanical consequences of marginal bone loss could be catastrophic particularly when the abutment screw is at supraosseous level. This study aimed at investigating marginal bone loss influence on the biomechanics of single implant crown using finite element (FE) analysis. Four FE models for a 3.5 × 13 mm implant supported by 4 bone levels (8.5 mm, 10 mm, 11.5 mm, and 13 mm) were subjected to 3 loading conditions: vertical, oblique, and horizontal. The results indicated 5-10 times increase in maximum von Mises stresses under oblique and horizontal loading. The maximum stresses within the fixture were concentrated at the bone/fixture interface with highest value under horizontal loading at 10 mm bone support. Abutment screw was most susceptible to fracture as the highest stress was concentrated at the screw/fixture interface. Cortical bone suffered its greatest stress level at the fixture/bone interface at 10 mm bone support. However, increasing bone support to 11.5 mm has improved the fracture resistance of the abutment screw to a great extent especially under oblique and vertical loading. Severe marginal bone loss might be attributed for abutment screw and fixture head fracture especially under horizontal loading.

Extrasinus zygomatic implant placement in the rehabilitation of the atrophic maxilla: three-dimensional finite element stress analysis.

Placement of zygomatic implants lateral to the maxillary sinus, according to the extrasinus protocol, is one of the treatment options in the rehabilitation of severely atrophic maxilla or following maxillectomy surgery in patients with head and neck cancer. The aim of this study was to investigate the mechanical behavior of a full-arch fixed prosthesis supported by 4 zygomatic implants in the atrophic maxilla under occlusal loading. Results indicated that maximum von Mises stresses were significantly higher under lateral loading compared with vertical loading within the prosthesis and its supporting implants. Peak stresses were concentrated at the prosthesis-abutments interface under vertical loading and the internal line angles of the prosthesis under lateral loading. The zygomatic supporting bone suffered significantly lower stresses. However, the alveolar bone suffered a comparatively higher level of stresses, particularly under lateral loading. Prosthesis displacement under vertical loading was higher than under lateral loading. The zygomatic bone suffered lower stresses than the alveolar bone and prosthesis-implant complex under both vertical and lateral loading. Lateral loading caused a higher level of stresses than vertical loading.

Stress analysis of occlusal forces in canine teeth and their role in the development of non-carious cervical lesions: abfraction.

Non-carious cervical tooth lesions for many decades were attributed to the effects of abrasion and erosion mainly through toothbrush trauma, abrasive toothpaste, and erosive acids. However, though the above may be involved, more recently a biomechanical theory for the formation of these lesions has arisen, and the term abfraction was coined. The aim of this study was to investigate the biomechanics of abfraction lesions in upper canine teeth under axial and lateral loading conditions using a three-dimensional finite element analysis. An extracted human upper canine tooth was scanned by µCT machine (Skyscan, Belgium). These µCT scans were segmented, reconstructed, and meshed using ScanIP (Simpleware, Exeter, UK) to create a three-dimensional finite element model. A 100 N load was applied axially at the incisal edge and laterally at 45° midpalatally to the long axis of the canine tooth. Separately, 200 N axial and non-axial loads were applied simultaneously to the tooth. It was found that stresses were concentrated at the CEJ in all scenarios. Lateral loading produced maximum stresses greater than axial loading, and pulp tissues, however, experienced minimum levels of stresses. This study has contributed towards the understanding of the aetiology of non-carious cervical lesions which is a key in their clinical management.