Phophi Kamposiora

Three-dimensional finite element analysis of stress-distribution around single tooth implants as a function of bony support, prosthesis type, and loading during function☆

The elastic limit of bone surrounding implants may be surpassed and thus produce microfractures in bone. The purpose of this study was to use computer simulations to examine clinical situations with IMZ implants in edentulous mandibles and to identify loading conditions that could lead to bone microfractures. Three-dimensional finite element analysis models were used to examine effects of: (1) types of edentulous mandibles, (2) veneering materials, (3) the absence of cortical bone, (4) different intramobile elements, (5) loading directions, and (6) loading levels. Stress distribution patterns were compared and interfacial stresses were monitored specifically at four heights along the bone-implant interface. Stresses were concentrated toward cortical bone (0.8 to 15.0 MPa). There were no differences between types of veneering materials and the absence of cortical bone increased interfacial stresses. The use of a titanium intramobile element decreased stresses. Minor stress increases were associated with smaller mandibles. Oblique loads increased stresses 15 times, and 200 N loads increased stresses 10 times. Conditions for bone microfracturing were associated with oblique loads, high occlusal stress magnitudes, and the absence of cortical bone.

3D-FEA of osseointegration percentages and patterns on implant-bone interfacial stresses.

OBJECTIVES The degree of osseointegration and its patterns are important for the success of implants. 3D-FEA was used to determine interfacial stresses on a single tooth implant (IMZ) for four degrees of osseointegration (100, 75, 50 and 25%), and five patterns at 50% osseointegration (locally alternating, coronal only, apical only, facial only and lingual only). METHODS The implant was restored with a metal-ceramic crown and subjected to 10 MPa axial or oblique applied stress. Resolved stresses were examined at four heights along the implant-bone interface. RESULTS The degree of osseointegration did not affect resolved stress levels or distributions. Oblique loads elevated interfacial stresses 5 to 20 times. Stresses were always higher at the bone crest. CONCLUSIONS Osseointegration patterns with crestal bone reduced both crestal and apical stresses. Apical only osseointegration produced much higher apical stresses. Crestal osseointegration and axial loads minimized overall stress.

Matching repeatability and interdevice agreement of 2 intraoral spectrophotometers

STATEMENT OF PROBLEM The visual determination of tooth color with standard shade guides is a subjective method of color communication, depending on variables such as the light source, the operator, and the tooth. The assessment of tooth color may be improved by the use of special devices such as colorimeters or spectrophotometers. However, the repeatability and the interdevice agreement of these devices have not been thoroughly investigated. PURPOSE The purpose of this study was to evaluate the effect of different illuminants (natural daylight, dental unit lamp, and daylight lamp) on the matching repeatability of 2 intraoral spectrophotometers (Easyshade and SpectroShade). MATERIAL AND METHODS The maxillary right central incisor and canine and the mandibular left central incisor of each of 10 dental students were measured by a single operator using both devices. The color of each tooth was assessed 3 times with each device under each of the 3 different illuminants (natural daylight, a dental unit lamp, and a daylight lamp). The device readings were expressed in Vitapan 3D-Master shade codes. Statistical analysis was performed and the level of agreement was assessed with the Spearman Correlation Coefficient. RESULTS A particularly high to moderate level of agreement among the readings made under natural daylight, a dental unit lamp, and a daylight lamp was observed for both devices (P<.01), suggesting that their matching repeatability was not completely satisfactory for clinical practice. A moderate and a moderate to high level of agreement was found among Easyshade readings when the 3 different illuminants were used. The level of agreement for the respective SpectroShade readings was particularly high to high (P<.001). A particularly low level of agreement was found among the respective Easyshade and SpectroShade readings performed under any of the illuminants tested (P<.05), suggesting poor interdevice reliability. CONCLUSIONS The matching repeatability of both devices under natural daylight, a dental unit lamp, and a daylight lamp was not completely satisfactory for clinical practice. The effects of different illuminants seem to be more pronounced for Spectroshade than for Easyshade. The interdevice agreement between the 2 devices tested was poor, suggesting that the 2 devices were not compatible.

Presentation of two cases of immediate restoration of implants in the esthetic region, using facilitate software and guides with stereolithographic model surgery prior to patient surgery.

Improvements in both implant microsurfaces and placement techniques have reduced healing time and increased survival rates. CAD/CAM technology and improved ceramic materials allow for achievement of improved esthetics at the implant restoration level. Two clinical procedures have the capacity to decrease patient postoperative discomfort and improve esthetics. Flapless surgery reduces surgical trauma and postoperative problems. Placement of the final prosthetic abutment at the time of implant placement stabilizes soft tissue adhesion and position to the implant. Both results require careful presurgical planning with precise implant and abutment placement. This is a clinical report of two cases that are part of a larger ongoing clinical trial of 20 patients. The inclusion criterion was that patients should be missing a single tooth in the esthetic zone. Facilitate™ software was used in conjunction with dicom files transferred from CT scans for diagnosis. Stereolithographic models and surgical guides were fabricated from the digital information. Surgical guides were used preoperatively so implant replicas could be placed in stereolithographic models as simulated surgery. A ZirDesign™ ceramic abutment was adapted on the model, and a provisional crown was fabricated. At the time of actual implant surgery, the same surgical guide was used with a flapless approach. The previously modified ceramic abutment was screw-retained and torqued to place into the implant. The provisional crown was then cemented after blocking out the screw access hole. A final restoration was fabricated from all-ceramic material after several months. Success requires careful patient selection and attention to each step of the technique. Preliminary outcomes from the ongoing clinical trial are promising.

Composition, phase analysis, biaxial flexural strength, and fatigue of unshaded versus shaded Procera zirconia ceramic

STATEMENT OF THE PROBLEM Recent interest in shaded zirconia has raised questions about the relative stability of the tetragonal phase after colorant oxide additions. PURPOSE The purpose of this in vitro study was to evaluate the effects of fatigue cycling on the stability of a commercially available dental zirconia (Procera) in both unshaded and shaded compositions by measuring the change in biaxial flexural strength (BFS) after 500 000 cycles at 80-N loads and in phase composition as detected by x-ray diffraction (XRD). MATERIAL AND METHODS Partially stabilized zirconia disks (NobelProcera) were fabricated in unshaded and shaded forms (12 mm diameter × 0.8 mm thick). Specimens were analyzed by energy-dispersive x-ray spectroscopy (EDS) and by wavelength-dispersive x-ray spectroscopy (WDS) for oxide compositions which indicated the presence of small amounts of Fe-O (0.13 ±0.10 wt %) in the shaded specimens. XRD focused on the tetragonal (T) and monoclinic (M) peaks in the 20 to 40 degrees 2θ range. The disks were polished on 1 side, cyclically loaded (80N, 500 000 cycles, custom 4-station fatigue test machine), and tested for residual BFS after cycling. Unshaded (U) and shaded groups (S) were compared before (U1, S1) and after (U2, S2) load cycling with XRD and residual BFS. RESULTS Residual BFS (MPa) for specimens before (U1=856 ±99 versus S1= 842 ±40) and after fatigue (U2=772 ±65 versus S2= 718 ±68) were statistically different (U1 versus U2; S1 versus S2; U2 versus S2, P<.05). The XRD of U1 and S1 specimens revealed tetragonal and cubic zirconia. U2 and S2 specimens contained tetragonal zirconia, with the initial appearance of small amounts of monoclinic zirconia after fatigue cycling. Monoclinic detection was measured on the tension side of the tested specimens and varied between tests at the center and radially at 4 mm. CONCLUSIONS The results indicated shaded materials more readily transform the tetragonal to the monoclinic phase during load cycling than unshaded ones. However, extrapolating the effects of any shortening of the service life of zirconia compositions is difficult. The potential mitigating effects of other factors such as the thermal postprocessing of porcelain veneers, stains on zirconia, or effects of water have yet to be investigated.

Cyclic Loading Effect on Color Stability of Unshaded versus Shaded Zirconia

STATEMENT OF PROBLEM Shaded versions of dental zirconia may improve initial color matching to teeth, but might change color with cyclic mechanical loading. PURPOSE The purpose of this study was to measure the color of unshaded and shaded zirconia dental ceramic before and after cyclic mechanical loading and calculate color differences (ΔE). MATERIAL AND METHODS Disk-shaped specimens (N = 30, Nobel Procera, 0.8 mm thick, 12 mm diameter) of unshaded or shaded zirconia (intrinsically shaded by small oxide modifications) were fabricated by the Nobel Biocare using standard CAD-CAM processing. Milled surfaces were polished. CIE L*a*b* values were measured (Konica Minolta spectrophotometer) before and after mechanical cycling (custom modified Leinfelder test machine, biaxial flexure loading, load = 80 N × 500,000 cycles, dry), and L*a*b* individual differences and ΔE color differences were calculated and compared (ANOVA, p < 0.05). RESULTS Mean L*a*b* values for the unshaded group before (U1 = 86.165, -0.887, 0.372) and after (U2 = 84.860, -0.805, 0.097) cyclic loading were compared to the shaded group before (S1 = 75.281, -0.679, 23.251) and after (S2 = 74.961, -1.233, 22.439) cyclic loading. All color variables for both unshaded and shaded groups were significantly different between before and after cyclic loading (p < .004) except for the L* value of the shaded group. The ΔE for unshaded (1.441 ± 0.495) versus shaded (1.252 ± 0.363) were statistically different but clinically the change would not be detectable at this point. CONCLUSIONS The color of the unshaded and shaded zirconia specimens was influenced by cyclic loading (p < 0.05). Color changes were detectable but small at levels up to 500,000 cycles, and remained clinically acceptable at that point. CLINICAL SIGNIFICANCE It is important to acknowledge any possible color changes that might occur in zirconia restorations, especially in the esthetic zone. Minor color changes that are individually imperceptible to the human eye within different restorative components may be compounded to produce clinically significant color change that is not aesthetically acceptable.

Intrasurgical implant position transfer and interim restoration placement.

In the esthetic zone, the placement of an interim prosthesis is an important stage in implant treatment for gingival contouring. This article presents a simple procedure for making an intraoperative implant position transfer to construct an interim prosthesis with optimal shape and emergence profile. This prosthesis, inserted at stage II surgery, guides soft tissue healing and aids in the fabrication of a definitive prosthesis with optimal gingival contours.

Osseointegration of Dental Implants in a Patient with Hajdu-cheney Syndrome

Background: Hajdu-Cheney Syndrome (HCS) is a rare hereditary bone metabolism disorder characterized by acro-osteolysis, short stature, craniofacial changes, periodontitis and premature tooth loss. Extensive search of the current literature revealed no reports of implant placement in patients with HCS. Case Report: A 22-year old woman with osteoporosis, generalized advanced chronic periodontitis and premature tooth loss was referred to the Postgraduate Clinic of Periodontology, University of Athens-Greece. The patient was diagnosed in 2001 with HCS. The patient received non-surgical periodontal treatment and several teeth were extracted due to extensive alveolar bone loss. After careful consideration of the possible implications deriving from the patient’s condition and having taken her young age into account, initially, a dental implant was placed in the upper right first premolar region. Specific protocols such as longer healing periods were implemented, so five years after placement and successful osseointegration of this implant, four additional dental implants were placed in the posterior regions of the maxilla and the mandible. Prosthetic rehabilitation followed 6 months after implant placement. Upon completion of periodontal treatment, the patient was enrolled in a periodontal maintenance program. Results: Clinical and radiographic examination of the patient during the periodontal maintenance program after implant placement revealed no abnormalities in the implant region. Conclusion: Patients with HCS suffer from periodontitis, bone destruction and premature tooth loss. This case indicates the successful osseointegration of dental implants in patients with HCS. However, further research is required in order to determine the predictability of dental implant placement in those patients.

A Case Series Treatment Outcome Report Following 5 Years of Implant Overdenture Treatment.

PURPOSE To assess clinical performance of bar-retained implant overdentures (IOs) with distally placed ERA attachments on four implants, and patient satisfaction after a follow-up period of 5 years in a convenience selection of 15 patients. MATERIALS AND METHODS Bar-retained IOs with distally placed ERA attachments were placed and clinically monitored. Encountered complications during a 5-year follow-up period were recorded; and a modified OHIP-14 questionnaire was used to assess patient satisfaction. RESULTS Implant and restoration survival rates of 97.5% and 100%, respectively, were recorded. The most common maintenance requirement was the replacement of ERA retentive elements. A high degree of patient satisfaction was reported. CONCLUSIONS The proposed IO design is a reliable clinical treatment protocol associated with a high degree of patient satisfaction and minor prosthetic complications.