Failure resistance of single-implant crowns assembled from polyetheretherketone and lithium disilicate abutments and different crown materials after artificial aging.

AIM: To investigate the effect of using different materials for the fabrication of implant abutments and crowns on the mechanical behavior of implant-supported single crowns after artificial aging. The materials were tested in different combinations to reveal whether using stiff or resilient materials as an abutment or a crown material might influence the fracture strength of the whole structure. MATERIALS AND METHODS: A total of 40 implants (blueSKY, bredent GmbH & Co. KG) were restored with identical custom-made CAD/CAM abutments milled out of lithium disilicate or ceramic-reinforced PEEK and were divided into 5 test groups (n = 8 each). Forty crowns made of three different materials (zirconia, lithium disilicate, and ceramic-reinforced PEEK) were used to restore the abutments. Specimens were subjected to mechanical load up to 1,200,000 cycles in a chewing simulator (Kausimulator, Willytech) with additional thermal cycling. The surviving specimens were subjected to quasi-static loading using a universal testing machine (Z010, Zwick). RESULTS: PEEK abutments with zirconia crowns showed the highest median failure load (3890.5 N), while PEEK abutments with lithium disilicate crowns exhibited the lowest (1920 N). Fracture and deformation occurred in both crowns and abutments. CONCLUSION: The failure load of the restorations was influenced by the material of the abutment and the crown. Restoring PEEK abutments with zirconia crowns showed a high failure load and no screw loosening.

Biomechanics of 3-implant-supported and 4-implant-supported mandibular screw-retained prostheses: A 3D finite element analysis study.

STATEMENT OF PROBLEM: The number of implants required for the rehabilitation of completely edentulous mandibles has been controversial. The use of a greater number of implants can produce favorable biomechanical outcomes. However, this will lead to high costs and may require complex surgical procedures. Therefore, the minimum number of implants that can produce desirable outcomes should be used. PURPOSE: The purpose of this 3D finite element study was to compare the biomechanics of mandibular 3-implant-supported to 4-implant-supported prostheses. The opposing occlusion was a maxillary complete denture or natural dentition. MATERIAL AND METHODS: Two finite element analysis mandibular anatomic models were created. Implants were virtually placed in the mandibular lateral incisor and second premolar region bilaterally in the 4-implant-supported prosthesis model. For the 3-implant-supported model, they were placed in the midline and bilaterally in the second premolar region. Screw-retained polymethyl methacrylate prostheses were designed. Reverse engineering was used to convert standard tessellation language files into computer-aided design solid models. Vertical and oblique loading was applied twice: simulating an opposing maxillary complete denture and a natural dentition. Von Mises stresses and equivalent strains generated in the peri-implant bone, implants' von Mises stresses and the maximum vertical displacement of the prosthesis were recorded. RESULTS: All recorded outcomes reported higher values for the 3-implant-supported prosthesis compared with the 4-implant-supported models for both applied loads. When opposed by a maxillary complete denture, maximum strain values for the 3-implant-supported (2.3×103 µÎµ) and 4-implant-supported (1.6×103 µÎµ) models were less than the different threshold limits for the bone resorption reported (3×103, 3.6×103, 6.6×103 µÎµ). When opposed by a maxillary natural dentition, maximum strain values for the 3-implant-supported (4.10×103 µÎµ) and 4-implant-supported (3.88×103 µÎµ) models were less than the highest reported threshold limit for bone resorption (6.6×103 µÎµ) in contrast with other reported threshold limits (3×103, 3.6×103 µÎµ). In both designs irrespective of the magnitude and direction of loading, the maximum recorded von Mises stresses of the implants (126 MPa) and denture displacement (3.24×102 µm) were less than titanium's yield strength of (960 to 1180 MPa) and the displacement values (5.2×103 to 8.8×103 µm) reported in the literature. CONCLUSIONS: When opposed by a complete denture, recorded biomechanical outcomes for the 3- and 4-implant-supported designs were within physiologic limits. When opposed by a natural dentition, the von Mises stresses of the implants and denture displacement values for both designs were within a favorable mechanical range, whereas peri-implant stresses and strain exceeded most reported physiologic tolerance levels of bone except for the 6.6×103 µÎµ threshold limit for the bone resorption reported.

Influence of Different CAD/CAM Crown Materials on the Fracture of Custom-Made Titanium and Zirconia Implant Abutments After Artificial Aging.

PURPOSE: To investigate the effects of different commercially available computer-aided design/computer-assisted manufacturing (CAD/CAM) materials for fabrication of molar crowns, including polyetheretherketone (PEEK), on the fracture strength and failure mode of custom-made titanium and zirconia abutments after artificial aging. MATERIALS AND METHODS: A total of 48 identical custom-made CAD/CAM abutments milled out of titanium or zirconia were divided into six test groups of eight specimens each. The groups were assigned as follows: titanium abutments restored with zirconia crowns (TiZ), with lithium disilicate crowns (TiL), or with PEEK crowns (TiP); zirconia abutments bonded to a titanium base and restored with zirconia crowns (ZrZ), with lithium disilicate crowns (ZrL), or with PEEK crowns (ZrP). The specimens were artificially aged in a chewing simulator for 1.2 million cycles of dynamic loading with simultaneous thermal cycling and then loaded to fracture in the universal testing machine. Shapiro-Wilk test was used to test for normality. One-way analysis of variance followed by post hoc analysis using Bonferroni test was used to detect statistically significant differences among groups. RESULTS: All specimens survived the artificial aging process simulating 5 years of clinical service. The fracture patterns and means of the fracture strength (N) varied between groups: TiZ = 4,926 N; TiL = 3,706 N; TiP = 3,878 N; ZrZ = 5,529 N; ZrL = 2,826 N; and ZrP = 3,967 N. CONCLUSION: Although the tested combinations showed different fracture patterns and loads, all tested abutment and crown materials and their different combinations could be considered to have fracture strengths suitable for clinical application.

Oral Health-Related Quality of Life in Single Implant Mandibular Overdenture Retained by CM LOC versus Ball Attachment: A Randomized Controlled Trial.

AIM: This randomised clinical study aimed to detect whether CMLOC attachment could improve Oral Health-Related Quality of Life (OHRQOL) when compared to ball attachment. METHODS: Eighty edentulous patients were recruited to receive a single symphyseal implant for mandibular overdenture, after three months, randomisation was done to divide them into two groups; Dalbo ball (control group) and Cendres and Metaux locator (CM-LOC) (intervention) attachments respectively, oral health impact profile for edentulous patients (OHIP-EDENT)questionnaire was recorded before implant placement, two weeks after pick up, at 3, 6, 9, and 12 months. RESULTS: Results revealed a lack of statistical significance between the two groups except for psychological discomfort at 2 weeks after pick-up (p-value = 0.029). CONCLUSION: Single implant overdenture is a simple, reliable treatment modality for treating edentulous mandible and both CM LOC and Ball attachments are good alternatives for such treatment modality.

Prognosis of dental implants in patients with low bone density: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Osteoporosis is a risk factor for implant success. Evidence for the prognosis of dental implants in patients with osteoporosis is still unclear. PURPOSE: The purpose of this systematic review was to compare implant success in patients with low versus normal bone density and to evaluate special techniques used to enhance implant success in these patients. MATERIAL AND METHODS: Searches were performed electronically in 4 databases (PubMed, LILACS, Cochrane, and Grey Literature) through July 2017 and manually to identify studies addressing the subject. Randomized and nonrandomized clinical trials and cohort studies were included. RESULTS: Eleven studies met the eligibility criteria, with a total of 1071 participants. Seven studies compared implant success in low and normal bone density, and 4 compared implant success in special and conventional techniques of implant placement. The risk of bias in the assessment of cohort studies was critical; of nonrandomized clinical trials, serious; and of randomized clinical trials, high. The meta-analysis showed no significant difference between implant survival in patients with low and normal bone density 5 years after implant placement. CONCLUSIONS: Implant survival in patients with low bone density seems to be feasible with special precautions. Implant placement using special adopted techniques might provide equivalent implant stability, survival, and marginal bone loss to normal bone. The quality of evidence is still unclear.