Dynamics of implant site preparation affecting the quality of osseointegrated implants in the maxillary aesthetic zone

PurposeThis study compared piezoelectric (PE) and conventional drills (CD) for maxillary aesthetic zone implant insertion.Material and methodsThis was a prospective split-mouth study. Implants were divided into two groups. Beds were prepared with CDs in group I and PE in group II. The implant stability quotient (ISQ) of the mechanical implant stability (MIS) was measured intraoperatively. The ISQ of the biological implant stability (BIS) was recorded at postoperative second and fourth months. Marginal bone loss (MBL) and bone density (BMD) were measured in the first and second years after prosthetic loading. The osteotomy time was also documented for both techniques. P values <0.05 were considered significant.ResultsSixty implants in 30 patients were included. PE provided a significantly higher ISQ. All values were above 70 throughout the follow-up period. The mean of the ISQ for MIS was 63.78 ± 1.03 and 73.89 ± 1.05 in group I and group II, respectively (p = 0.003). PE needed significantly longer osteotomy time with a mean of 11.99 ± 0.839 min. The BIS quality had high stability in group II and medium stability in group I throughout the study period. Its values decreased in both groups. Group II had a lesser percentage of decrease. However, it was significant only at time intervals between intraoperative and two months' postoperative (p = 0.004). MBL and BMD demonstrated insignificant results.ConclusionThe implant site preparation with PE devices should be preferred to CDs whenever possible, because they seem to enhance implant stability and osseointegration, especially at the initial stages of healing.     

Influence of implant scanbody material,position and operator on the accuracy of digital impression for complete-arch: A randomized in vitro trial

PurposeTo evaluate the influence of implant scanbody (ISB) material, position and operator on the accuracy of a confocal microscopy intraoral scanning (IOS) for complete-arch implant impression.MethodsAn edentulous maxillary model with 6 internal hexagonal connection analogues was scanned with an extraoral optical scanner to achieve a reference file. Three ISBs made of different materials (polyetheretherketone (Pk), titanium (T) and Pk with a titanium base (Pkt)) were scanned with IOS by 3 operators. The resulting 45 test files were aligned to the reference file with a best fit algorithm. Linear (ΔX, ΔY and ΔZ-axis) and angular deviations (ΔANGLE) were assessed. Absolute values of the linear discrepancies were summed up to obtain a global measure of linear absolute error (ΔASS). Influence of ISB material, position and operator was statistically assessed using the mixed general linear model.ResultsAt multivariate analysis, whenΔASS was considered as response variable, it was identified a significant influence of material (p < 0.0001) and position (p = 0.0009) while no significant operator effect was detected.When ΔANGLE was considered as response variable, material and position significantly influenced the expected ΔANGLE (p = 0.0232 and p < 0.0001) and no operator effect was identified.ConclusionsThe investigated IOS for complete-arch digital impression was influenced by the ISB material with peek reporting the best results on both linear and angular measurements followed by titanium, peek-titanium resulting as the less accurate. Implant angulation affected significantly the linear deviations while implant position the angular deviations. Operator did not show any significant effect on the IOS accuracy.     

Effects of predegeneration on nerve regeneration through silicone Y-chambers

The effects of nerve predegeneration on the preferential growth of regenerating axons were studied using a silicone Y-chamber model. This system provided a choice for axons to grow towards two distal nerve options, either a 7-day predegenerated nerve segment (PNS) or a fresh nerve segment (FNS). The rat peroneal or tibial nerve was inserted into the proximal intlet and the PNS and FNS of the corresponding nerve were inserted into the distal outlets. At 28 days postoperative, the size of the distal regenerate was significantly greater (26%) towards the PNS for the tibial nerve group. The density and number of regenerated myelinated axons in the distal nerve segment was greater on the PNS for both the tibial (97 and 88%, respectively) and peroneal (221 and 221%, respectively) nerve groups. In contrast, the elevated density and number of nonvascular nuclei was relatively constant for both PNS and FNS. Immunocytochemical and ultrastructural evidence support the hypothesis that the early activation of Schwann cells is primarily responsible for the enhanced regeneration and maturation observed in PNS. It is suggested that PNS might improve the outcome after clinical repair of injured peripheral nerves.     

尼尔雌醇皮埋剂保护去卵巢大鼠的骨量

目的：探讨尼尔雌醇（NYL）皮埋剂对卵巢切除（OVX）大鼠骨量的影响。为长期雌激素替代治疗提供一种新的选择。方法：用DEXA分别测定假手术（Sham）组、卵巢切除（OVX）组、卵巢切除加左炔诺孕酮皮埋剂（LNG）组、卵巢切除加LNG皮埋剂和NYL皮埋剂（LNG＋NYL）组及OVX加NYL皮埋剂（NYL）组大鼠的活体和离体骨密度（BMD），并对血清碱性磷酸酶（ALP）和尿吡啶啉／肌酐（Pyr/Cr)进行检测。结果：与Shasm组比较，OVX组和LNG组大鼠全身，腰椎活性BMD和腰椎，股骨整体及各兴趣区（除第3兴趣区）、胫骨整体及干骺端第1兴趣区离体BMD均显著下降（P＜0．05－P＜0．01），而血清ALP和尿Pyr/Cr增高，后者差异有显著性（P＜0．05）。LNG＋NYL皮埋剂组和NYL皮埋剂组BMD较OVX组增加，在许多部位差异有显著性（P＜0．05－P＜0．01），BMD与Sham组接近，而它们的血清ALP和尿Pyr/Cr较OVX组下降（P＜0．05－P＜0．01）。结论：LNG皮埋剂不能阻止OVX导致的骨丢失，NYL皮埋剂有保护OVX大鼠骨量的作用。     

Fracture Resistance of Yttria-Stabilized Zirconia Dental Implant Abutments

Purpose: An in vitro study was performed to assess the effect of different degrees of clinical reduction of zirconia abutments on the failure load of clinical assemblies.
Materials and Methods: Zirconia abutments (Y-TZP Ceramic Abutment, Astra Tech) were prepared with 0, 0.5, or 1 mm of external axial reduction starting 1 mm above the height-of-contour. Abutments (n = 10) were attached to implant analogs (25 Ncm torque) embedded in a stainless steel cylinder using Field's metal. Fracture loads (N) were determined when assemblies were loaded at 60° off-axis until failure (Instron, CHS = 0.1 mm/min). Groups were statistically compared using ANOVA ( p < 0.05).
Results: Fracture loads for all assemblies displayed large variations within groups. There were no statistically significant differences ( p > 0.05) among different abutment groups with a mean fracture load of 429 N (±140) for the control group, 576 N (±120) for 0.5-mm margins, and 547 (±139) for 1.0-mm margins. All fractures occurred at the interface where the abutment was connected to the analog.
Conclusion: In this in vitro study of simulated ultimate assembly strength, the preparation of zirconia abutments did not significantly impair the fracture resistance of simulated implant assemblies. All implant abutments fractured at rates higher than the maximum incisal forces (90–370 N) estimated to occur in the anterior region of the mouth.     

The implications of stress patterns in the vertebral body under axial support of an artificial implant

Clinical studies show an association between changed load patterns both in the disc and its adjacent vertebral body, with painful degenerated discs. This suggests that failure to restore the normal loading pattern on implantation of a disc replacement could be a cause of lower clinical success rate. In the present study the variations of load patterns in the vertebra after disc implantation was studied using a simplified finite element models of natural and artificial discs. The effect of implant size and presence of voids at the implant–bony endplate interface were studied, for the worst case scenario of no bone remodelling. An altered stress pattern was observed in the vertebrae of implanted segments. The use of smaller size implants and presence of voids at the interface caused localized stress concentration in the endplate and adjacent cancellous bone. The study results support the hypothesis that current implants fail to restore normal loading patterns in the vertebral body, and the localized high stress regions could be the source of pain, and the cause of low success rate of TDRs.     

Screw fixation to the posterior cortical shell does not influence peak torque and pullout in anterior cervical plating

There is no consensus over whether screw fixation for anterior cervical plating should include the posterior cortical shell of the vertebral bodies or not. Thus, the purpose of this study was to investigate the function of the posterior cortical shell with respect to maximal screw torque and pullout force. Twenty-four fresh frozen human cervical vertebrae coming from six spinal segments C4-C7 were used. They were scanned for bone mineral density (BMD) and then assigned to two groups with comparable bone density and segmental distribution. The posterior longitudinal ligament was resected carefully and two parallel burr holes were drilled into each vertebral body. The posterior cortical shell was removed in one burr hole, using a 6-mm steel burr, producing a shallow excavation with a depth of approximately 2 mm. An ABC screw was inserted into each burr hole. The screw to be inserted into the hole with the posterior excavation was called "monocortical". In contrast, the contralateral screw was called "bicortical". Peak torque was measured in one group, while pullout force was analyzed using the specimens of the second group. Mean value and standard deviation were calculated for peak torque and pullout force with respect to the type of fixation. A paired t-test was used to determine the effect of fixation type on peak torque and pullout force. Pearson moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force with respect to whether the screw was "mono- or bicortical". A 95% level of significance was used for all tests. No significant differences for peak torque and pullout force could be found comparing monocortical and bicortical screw fixation. However, for both monocortical and bicortical screw fixation, a positive correlation was seen for peak torque versus BMD and for pullout force versus bone mineral density, respectively. The importance of the posterior cortical shell for screw pullout force and screw peak torque seems to be negligible. In constrast, BMD greatly influences both peak torque and pullout force for both types of fixation.     

Comprehensive Biocompatibility Testing of a New Semirigid Titanium Spine Implant in Vitro

Background: Titanium spine implants are well established materials in posterior spondylodesis. The biocompatibility of a semirigid tivanium cable suitable for pedicle screws in posterior spinal fusion (DDS-Plus^?) was tested by a human bone marrow cell culture. In comparison to the tivanium cable implant (Ti6Al4V; DDS-Plus^?), hydroxyapatite (HA), commercially pure titanium (cpTi), glass, chromium-cobalt alloy, (CrCoMo), polyaryletherketon (PAEK) and polyethylene (UHMW-PE) were tested. Materials and Methods: Scanning electron microscopy (SEM), SEM-energy dispersive X-ray analysis (SEM-EDX), fluorescent activated cell sorter (FACS), immunohistochemical techniques, light microscopy (LM) and immunochemical extracellular matrix analysis served to judge the in vitro biocompatibility of the different implants in a human bone marrow cell culture. Results: The datas of this investigation point out that the tivanium cable is equally biocompatible to commercially pure titanium and showed less signs of cytotoxicity than the other tested materials in vitro. Beside the titanium alloys, HA showed a high degree of biocompatibility compated to the polymers and CrCoMo too. Conclusions: In respect to their in vitro biocompatibility, the semirigid tivanium spine cable could be an alternative for other systems for posterior spondylodesis. Biomechanical and clinical studies are necessary to improve these datas. Received: March 29, 2002; revision accepted: September 30, 2002 Correspondence Address Marcus J?ger, MD, Department of Orthopedics, Heinrich Heine University, 40225 Duesseldorf, Moorenstra?e 5, Germany, Phone (+49/211) 8117960, Fax (+49/202) 9422623, e-mail: drjaegermarcus@yahoo.de