Numerical assessment of bone remodeling around conventionally and early loaded titanium and titanium-zirconium alloy dental implants.

The aim of this study was to investigate conventionally and early loaded titanium and titanium-zirconium alloy implants by three-dimensional finite element stress analysis. Three-dimensional model of a dental implant was created and a thread area was established as a region of interest in trabecular bone to study a localized part of the global model with a refined mesh. The peri-implant tissues around conventionally loaded (model 1) and early loaded (model 2) implants were implemented and were used to explore principal stresses, displacement values, and equivalent strains in the peri-implant region of titanium and titanium-zirconium implants under static load of 300 N with or without 30° inclination applied on top of the abutment surface. Under axial loading, principal stresses in both models were comparable for both implants and models. Under oblique loading, principal stresses around titanium-zirconium implants were slightly higher in both models. Comparable stress magnitudes were observed in both models. The displacement values and equivalent strain amplitudes around both implants and models were similar. Peri-implant bone around titanium and titanium-zirconium implants experiences similar stress magnitudes coupled with intraosseous implant displacement values under conventional loading and early loading simulations. Titanium-zirconium implants have biomechanical outcome comparable to conventional titanium implants under conventional loading and early loading.

A pilot study of joint stability at the zirconium or titanium abutment/titanium implant interface.

PURPOSE: To compare the interfaces of loaded and unloaded zirconium and titanium abutments with titanium implants using scanning electron microscopy (SEM). MATERIALS AND METHODS: Zirconium and titanium abutments (n = 5 per group; four test and one control) were torque-tightened into titanium implants secured into metal blocks, and computer-aided design/computer-assisted manufacture-based zirconium oxide copings were fabricated and cemented to the abutments with temporary resin-based cement. Specimens of each restoration were subjected to cyclic axial and lateral loading of 30 N at 2 Hz for 500,000 cycles using a servohydraulic test system; control specimens were left unloaded. Then, the abutment/implant assemblies were embedded in acrylic resin, sectioned longitudinally along the midline, and inspected under SEM with x-ray microanalysis. RESULTS: Loosening or fracture of the copings and implant components was not observed after dynamic loading in both groups. SEM and x-ray microanalysis revealed unexpected microleakage of acrylic resin at the interface. Acrylic resin in the implants tightened to the titanium abutments was limited to the cervical part, and the components displayed scratched and smashed regions, suggesting slight deformation of the implant neck. Microleakage and pooling of acrylic resin were observed approaching the screw joint in loaded implants tightened to zirconia abutments, and the amount of microleakage was greater than in the unloaded control specimens, which had a larger microgap than the titanium abutment/titanium implant interface. Loaded zirconia abutments were associated with wear, scratches, and, in one sample, chipping. CONCLUSIONS: Zirconium abutment/titanium implant interface may be susceptible to wear of the abutment coupled with deformation of the implant neck greater than that associated with the conventional titanium abutment/titanium implant interface under dynamic loading.

The effects of pulsed electromagnetic field (PEMF) on osteoblast-like cells cultured on titanium and titanium-zirconium surfaces.

BACKGROUND: Commercially pure Ti, together with Ti Ni, Ti-6Al-4V, and Ti-6Al-7Nb alloys, are among the materials currently being used for this purpose. Titanium-zirconium (TiZr) has been developed that allows SLActive surface modification and that has comparable or better mechanical strength and improved biocompatibility compared with existing Ti alloys. Furthermore, approaches have targeted making the implant surface more hydrophilic, as with the Straumann SLActive surface, a modification of the SLA surface. PURPOSE: The aim of this study is to evaluate the effects of pulsed electromagnetic field (PEMF) to the behavior of neonatal rat calvarial osteoblast-like cells cultured on commercially pure titanium (cpTi) and titanium-zirconium alloy (TiZr) discs with hydrophilic surface properties. MATERIALS AND METHODS: Osteoblast cells were cultured on titanium and TiZr discs, and PEMF was applied. Cell proliferation rates, cell numbers, cell viability rates, alkaline phosphatase, and midkine (MK) levels were measured at 24 and 72 hours. RESULTS: At 24 hours, the number of cells was significantly higher in the TiZr group. At 72 hours, TiZr had a significantly higher number of cells when compared to SLActive, SLActive + PEMF, and machine surface + PEMF groups. At 24 hours, cell proliferation was significantly higher in the TiZr group than SLActive and TiZr + PEMF group. At 72 hours, TiZr group had higher proliferation rate than machine surface and TiZr + PEMF. Cell proliferation in the machine surface group was lower than both SLActive + PEMF and machine surface + PEMF. MK levels of PEMF-treated groups were lower than untreated groups for 72 hours. CONCLUSIONS: Our findings conclude that TiZr surfaces are similar to cpTi surfaces in terms of biocompatibility. However, PEMF application has a higher stimulative effect on cells cultured on cpTi surfaces when compared to TiZr.

CAD/CAM glass ceramics for single-tooth implant crowns: a finite element analysis.

PURPOSE: To evaluate the load distribution of CAD/CAM mono-ceramic crowns supported with single-tooth implants in functional area. MATERIALS AND METHODS: A 3-dimensional numerical model of a soft tissue-level implant was constructed with cement-retained abutment to support glass ceramic machinable crown. Implant-abutment complex and the retained crown were embedded in a Ø 1.5 × 1.5 cm geometric matrix for evaluation of mechanical behavior of mono-ceramic CAD/CAM aluminosilicate and leucite glass crown materials. Laterally positioned axial load of 300 N was applied on the crowns. Resulting principal stresses in the mono-ceramic crowns were evaluated in relation to different glass ceramic materials. RESULTS: The highest compressive stresses were observed at the cervical region of the buccal aspect of the crowns and were 89.98 and 89.99 MPa, for aluminosilicate and leucite glass ceramics, respectively. The highest tensile stresses were observed at the collar of the lingual part of the crowns and were 24.54 and 25.39 MPa, respectively. CONCLUSION: Stresses induced upon 300 N static loading of CAD/CAM aluminosalicate and leucite glass ceramics are below the compressive strength of the materials. Impact loads may actuate the progress to end failure of mono-ceramic crowns supported by metallic implant abutments.

Comparative assessments, meta-analysis, and recommended guidelines for reporting studies on histomorphometric bone-implant contact in humans.

PURPOSE: To evaluate factors that have an influence on histomorphometric bone-to-implant contact (BIC) of dental implants in humans. MATERIALS AND METHODS: Using inclusion/exclusion criteria, eligible studies were searched in five databases and handsearched in 11 journals. A total of 351 articles were assigned to full text analysis. The extracted data were assigned to comparative statistical assessments and meta-analysis. RESULTS: A total of 55 articles were included in the analysis. The mean BIC found in comparative assessments and meta-analysis of implants in the mandible (70.97 and 69.744 ± 3.304, respectively) was higher than those in the maxilla (53.24 and 56.692 ± 3.598; P = .000 and P = .008, respectively). The mean BIC in the anterior mandible (79.42) and maxilla (74.19) were higher than the posterior mandible (69.14) and maxilla (36.68) (P < .05). Differences were detected in BIC of commercially available implants and experimental micro-implants (P < .05). Comparative assessments and meta-analysis showed that conventionally loaded implants (75.70 and 75.786 ± 4.889, respectively) had higher BIC than unloaded (54.07 and 53.24 ± 4.971, respectively) and immediately loaded implants (58.53 and 68.831 ± 4.972; P = .000 and P = .004, respectively). CONCLUSIONS: Based upon a meta-analysis of the literature the following conclusions can be made: The BIC in the mandible is higher than the maxilla. The BIC is higher in the anterior than the posterior regions. The implant design coupled with the anatomical region affects the amount of BIC. Placement of experimental micro-implants with different surfaces in the posterior region always result in low and almost comparable BIC. The loading state and healing period seems to have an influence on BIC. Specific reporting guidelines are required to improve reporting of studies on human BIC.

Predicting bone remodeling around tissue- and bone-level dental implants used in reduced bone width.

The objective of this study was to predict time-dependent bone remodeling around tissue- and bone-level dental implants used in patients with reduced bone width. The remodeling of bone around titanium tissue-level, and titanium and titanium-zirconium alloy bone-level implants was studied under 100 N oblique load for one month by implementing the Stanford theory into three-dimensional finite element models. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x- and y- axes of the implant were evaluated. Maximum and minimum principal stresses around tissue-level implant were higher than bone-level implants and both bone-level implants experienced comparable stresses. Total strain energy density in bone around titanium implants slightly decreased during the first two weeks of loading followed by a recovery, and the titanium-zirconium implant showed minor changes in the axial plane. Total strain energy density changes in the loading and contralateral sides were higher in tissue-level implant than other implants in the cortical bone at the horizontal plane. The displacement values of the implants were almost constant over time. Tissue-level implants were associated with higher stresses than bone-level implants. The time-dependent biomechanical outcome of titanium-zirconium alloy bone-level implant was comparable to the titanium implant.

Early-loaded one-stage implants retaining mandibular overdentures by two different mechanisms: 5-year results.

PURPOSE: To compare the biologic and prosthetic outcomes of implants loaded early to retain mandibular overdentures by means of two different attachment systems. MATERIALS AND METHODS: Patients were screened according to specific inclusion/exclusion criteria and randomly allocated to treatment groups involving two-implant-supported early loaded mandibular overdentures retained by ball attachments or Locator attachments. Marginal bone loss, Plaque Index, peri-implant infection, Bleeding Index, prosthetic complications, and Kaplan-Meier survival estimates of the groups were assessed at the 5-year recall. RESULTS: Among the 29 patients (58 implants) who completed the study, one implant was lost during healing; all implants survived after prosthesis delivery. Bone loss in the ball attachment group (0.77 ± 0.05 mm) was significantly greater than that in the Locator group (0.59 ± 0.03 mm). The Plaque and Bleeding indices of both groups were comparable, and peri-implant inflammation scores in both groups were zero for all implants. The frequencies of activation of the matrix, replacement of the matrix, and denture reline in the ball attachment group were significantly higher than those observed in the Locator group. While assessments for the absence of any complication showed that the 1- and 3-year Kaplan-Meier survival probabilities of both groups were comparable, when activation of the retainer was excluded, survival probabilities of the ball attachment group were higher. CONCLUSIONS: The biologic outcomes of early loaded mandibular overdentures retained by ball attachments or Locators were comparable. Although the frequency of prosthetic complications with ball attachments was higher, this did not decrease the survival probability for the treatment.

A prospective, open-ended, single-cohort clinical trial on early loaded Titanium-zirconia alloy implants in partially edentulous patients: up-to-24-month results.

PURPOSE: To evaluate biologic and prosthetic outcomes of titanium-zirconia alloy implants supporting fixed prostheses. MATERIALS AND METHODS: A total of 52 titanium-zirconia alloy implants were placed in 23 consecutive patients with partial edentulism. All implants were subjected to an early loading protocol by means of single-unit or up-to-four-unit fixed partial prostheses and observed between 7 and 24 months. The radiographic marginal bone loss and peri-implant soft tissue scores (Plaque Index, Bleeding Index, and Calculus Index) were recorded. In addition, prosthetic complications were recorded during the period of the study. RESULTS: Early or late implant failures were not observed, resulting in 100% implant survival and success of the implants. No prosthetic complications were observed. The mean (standard deviation) of marginal bone loss for 52 implants was 0.315 mm (0.24 mm). There were no signs of excessive bone loss with or without swelling or suppuration of the peri-implant soft tissue, and the soft tissue scores indicated good soft tissue integration. CONCLUSIONS: Titanium-zirconia alloy implants supporting fixed prostheses showed optimum radiographic, clinical, and prosthetic outcomes in an up-to-24-month assessment period.

Immediate versus conventional loading of implant-supported maxillary overdentures: a finite element stress analysis.

PURPOSE: To compare biomechanical outcomes of immediately and conventionally loaded bar-retained implant-supported maxillary overdentures using finite element stress analysis. MATERIALS AND METHODS: Finite element models were created to replicate the spatial positioning of four 4.1 × 12-mm implants in the completely edentulous maxillae of four cadavers to support bar-retained overdentures with 7-mm distal extension cantilevers. To simulate the bone-implant interface of immediately loaded implants, a contact situation was defined at the interface; conventional loading was simulated by "bonding" the implants to the surrounding bone. The prostheses were loaded with 100 N in the projected molar regions bilaterally, and strain magnitudes were measured at the buccal aspect of bone. RESULTS: The amplitude of axial and lateral strains, the overall strain magnitudes, and the strain magnitudes around anterior and posterior implants in the immediate loading group were comparable to those seen in the conventional loading group, suggesting that the loading regimens created similar stress/strain fields (P > .05). CONCLUSIONS: Conventional and immediate loading of maxillary implants supporting bar-retained overdentures resulted in similar bone strains.

Low-level laser therapy vs. pulsed electromagnetic field on neonatal rat calvarial osteoblast-like cells.

To compare the effects of pulsed electromagnetic field (PEMF) and low-level laser therapy (LLLT) on osteoblast cells in a cell culture model. Fifty thousand neonatal rat calvarial osteoblast-like cells per milliliter were seeded and 0.06 mT PEMF, 0.2 mT PEMF, and LLLT at 808 nm were applied for 24 and 96 h on the cells. To evaluate cellular proliferation and differentiation, specimens were examined for DNA synthesis, alkaline phosphatase (ALP) activity, cell numbers, and viability of the cells. Morphological appearances of the cells were observed using scanning electron microcopy after 24 and 96 h of incubation. At 24 and 96 h, the control group had a higher cell proliferation than 0.06 and 0.2 mT PEMF groups (p=0.001). At 96 h, 0.2 mT PEMF group had higher cell proliferation rate than 0.06 mT PEMF and LLLT groups (p=0.001). The cell count and cell viability in 0.2 mT PEMF group were higher than the 0.06-mT PEMF and LLLT groups, although these differences were not statistically significant at 96 h (p>0.05). At 24 and 96 h, cell viability in the control group was higher than the test groups. Alkaline phosphatase levels of the groups were comparable in both time intervals (p>0.05). 0.2 mT PEMF application on osteoblast-like cells led to cell proliferation and differentiation better than 0.06 mT PEMF and LLLT at 808 nm, although a remarkable effect of both PEMF and LLLT could not be detected. The ALP activity of 0.2 and 0.06 mT PEMF and LLLT were comparable.

Biomechanics of implant-tooth supported prostheses: effects of mesiodistal implant angulation and mode of prosthesis connection.

PURPOSE: The purpose of this study was to explore the effects of implant angulation and its possible influence on prosthetic connection as regards implant/tooth strains in a combined implant and natural tooth abutment fixed partial denture. METHODS: A natural tooth was embedded between vertically-aligned and 17° angulated implants in a polymethyl methacrylate acrylic resin model. Three designs (Group 1: tooth and vertically-aligned implant; Group 2: tooth and 17° angulated implant, Group 3: tooth and vertically-aligned implant having a different prosthetic connection to Group 1) of tooth-implant supported prostheses (n=4) were fabricated. Strain gauges were bonded on the prostheses and on the approximal sides of the natural tooth abutment and implants. Once the test fixed partial dentures were seated, a static load of 150 N was applied to each prosthesis. During testing, strain-gauge signals were digitalized by a data acquisition system and this signal was stored and assessed with corresponding software at a sample rate of 10 KHz. RESULTS: The data were then evaluated using Mann-Whitney U and Kruskal Wallis tests at 95% confidence level. Mesiodistal tilting of implants increased peri-implant strains in implant-tooth supported prostheses during torque-tightening and under load. The mode of prosthesis connection may affect strains within the prosthesis and natural tooth abutments, although its impact under static loading conditions seems negligible. CONCLUSIONS: This investigation suggests that mesiodistal tilting of implants may have a biomechanical effect in tooth-implant supported prostheses.

Do resin cements alter action potentials of isolated rat sciatic nerve?

OBJECTIVES: The purpose of this study was to explore the effects dual-cure resin cements on nerve conduction. METHODS: Panavia F, RelyX ARC, and Variolink II polymerized either by light-emitting diode (LED) or quartz tungsten halogen (QTH) were used in the study (n=10). The conductance of sciatic nerves of 50 rats were measured before and after contact with the specimens for 1 h. RESULTS: The time-dependent change in nerve conductance and the comparison of LED versus QTH showed that differences between groups are significant (P<.05). For both polymerization techniques, pair-wise comparisons of resin cements showed that the nerve conductance between groups is different (P<.05). RelyX ARC elicited irreversible inhibition of compound action potentials (more than 50% change) and Panavia F and Variolink II polymerized by LED and QTH did not alter nerve conduction beyond physiologic limits. CONCLUSIONS: Resin cements may alter nerve conductance and even lead to neurotoxic effects.

A randomized controlled clinical trial of feldspathic versus glass-infiltrated alumina all-ceramic crowns: a 3-year follow-up.

PURPOSE: The aim of this randomized controlled clinical trial was to compare the outcome of feldspathic porcelain (group 1) and glass-infiltrated alumina all-ceramic (group 2) crowns. MATERIALS AND METHODS: Patients were recruited based on inclusion/exclusion criteria, and 33 eligible subjects were assigned randomly to one of the two treatment groups. One hundred one crowns were placed predominantly in the anterior portion of the mouth and were cemented using resin cement. A baseline California Dental Association quality evaluation was completed, and Plaque and Gingival Index scores were recorded. Prosthetic and soft tissue scores were recorded for up to 3 years. RESULTS: Five restorations experienced mechanical failure. Kaplan-Meier analysis showed that the 3-year survival probabilities for group 1 (0.94) and group 2 (0.95) restorations were comparable (P = .484). Plaque and Gingival Index scores for both groups were similar at the 3-year recall (P > .999). Marginal integrity, anatomical form, and color and surface scores were also similar for both groups (P > .05). CONCLUSION: Feldspathic and glass-infiltrated alumina all-ceramic crowns placed predominantly in the anterior portion have comparable biologic and prosthetic outcomes, as well as survival probabilities.

Astra Tech, Brånemark, and ITI implants in the rehabilitation of partial edentulism: two-year results.

PURPOSE: To explore the soft tissue, marginal bone, and prosthetic complications (if any) of Astra Tech, Brånemark, and ITI implants supporting fixed prostheses during an observation period of 2 years. MATERIALS: The study comprised 26 patients, who received 42 Astra Tech, 36 Brånemark, and 29 ITI implants. After 3 months of healing, abutment connections were performed for Astra Tech and Brånemark implants, and fixed prostheses were delivered to the patients at 4 months. At 6-month, 1-year, and 2-year recall appointments, plaque index, periimplant inflammation index, and bleeding index scores, were recorded. The marginal bone levels were also measured at 2-year recall by means of radiographic evaluation, and prosthetic complications were recorded throughout the study. RESULTS: All implants survived during the 2-year observation period. The plaque index and periimplant inflammation index scores around Brånemark implants were higher than ITI and Astra Tech implants in the first year of function (P > 0.05). Marginal bone loss around ITI and Astra Tech implants was similar at 2 years (P > 0.05). The marginal bone loss around Brånemark implants was higher than Astra Tech implants (P < 0.05) but similar to ITI implants at 2-year recall appointment (P > 0.05). Fixed prostheses supported by ITI and Astra Tech implants did not experience prosthetic complications, and only 1 patient of the Brånemark group had porcelain veneer fracture. CONCLUSIONS: Astra Tech, Brånemark, and ITI implants supporting fixed prostheses had same survival rates (100%) in this study. ITI and Astra Tech implants had similar changes in marginal bone levels, whereas Brånemark implants had higher marginal bone loss, particularly in the first year of function.

Spontaneous early exposure and marginal bone loss around conventionally and early-placed submerged implants: a double-blind study.

PURPOSE: The aim of this retrospective study was to compare the frequency of spontaneous early exposure of cover screws and marginal bone resorption in conventionally and early-placed submerged implants before second-stage surgery. MATERIALS AND METHODS: A total of 103 Nobel Biocare Branemark implants were conventionally (Group 1), or early-placed (Group 2) in 46 consecutive patients following the two-stage surgical protocol. Patients in both groups received oral hygiene training in self-performed plaque control measures, including exposure of cover screws during healing. Spontaneous cover screw exposure (CSE) of each implant was recorded for both groups and scored from Class 0 (no perforation) to Class 4 (complete exposure). Plaque index scores were recorded and marginal bone-level (MBL) changes were measured in radiographs before second-stage surgery in a blind manner. RESULTS: MBL in Group 2 was higher than Group 1 in patients with or without interim prosthesis (P<0.05). The use of interim prosthesis did not increase MBL in Group 1, but led to higher MBL in Group 2. The percentage of non-exposed implants in Group 1 was higher than Group 2 (P=0.007, odds ratio=7). Group 1 implants had 11.5 times greater plaque index score 0 than those in Group 2 (P=0.031, odds ratio=11.5). The differences between MBL with regard to CSE scores 0 and 1-4 was significant for both sides in Group 2 and the mesial side in Group 1 (P<0.05). The difference between MBL with regard to plaque index scores 1-3 was similar in both groups (P>0.05). CONCLUSIONS: There is a direct relation between spontaneous early cover screw perforations with early crestal bone loss. Early-placed implants experienced more spontaneous perforations and associated bone loss in comparison with conventionally placed submerged implants. The use of interim dentures may lead to more CSE and consequent MBL in the early-placement protocol.

A systematic review of marginal bone loss around implants retaining or supporting overdentures.

PURPOSE: To evaluate, through a systematic review of the literature, the effects of implant design and attachment type on marginal bone loss in implant-retained/supported overdentures. MATERIALS AND METHODS: With the combined search terms "implant and overdenture," "implant-supported overdenture," "implant-retained overdenture," and "implant-anchored overdenture," along with specific inclusion and exclusion criteria, eligible articles between 1997 and 2008 (up to April 1) were retrieved from PubMed, EMBASE, OVID, the Cochrane Library databases, and seven journals by hand searching. Marginal bone loss values with regard to time, attachment type, and implant system used were compared by Kruskal-Wallis tests. Means and standard deviations of data were combined using fixed- and random-effect models and evaluated using meta-analysis. RESULTS: Forty-six articles were included in the analyses; data extraction and meta-analysis were able to be conducted on eight studies. Data regarding maxillary overdentures could not be analyzed statistically. Bone loss around mandibular implants did not seem to be influenced by implant system or attachment design (bar, ball, magnet, and other types) in the first year, from 1 to = or < 5 years, and even after 5 years (P > .05). Meta-analysis could not detect differences in implant systems or attachment types (P > .05). CONCLUSIONS: Based upon a systematic review and meta-analysis of the literature that identified a total of 4,200 implants from 13 manufacturers, there was no difference in marginal bone loss around implants retaining/supporting mandibular overdentures relative to implant type or attachment designs.

Systematic review of prosthetic maintenance requirements for implant-supported overdentures.

PURPOSE: To evaluate prosthetic maintenance requirements for implant-retained/supported overdentures via a review of the literature. MATERIALS AND METHODS: Using the combined search terms "implant and overdenture," "implant-supported overdenture," "implant-retained overdenture," and "implant-anchored overdenture," along with specific inclusion and exclusion criteria, eligible articles between 1997 and 2008 (up to April 1) were retrieved from PubMed, EMBASE, OVID, the Cochrane Library databases, and seven journals by hand-searching. The initial search yielded 3,120 titles, and 287 articles were assigned to full-text analysis. Upon classification of the prosthetic complications with regard to the jaws treated and the attachment systems used, within- and between-group comparative frequency analyses were undertaken with the Kruskal-Wallis test or the Mann-Whitney U test at P < .05. RESULTS: A total of 49 articles were included. Within- and between-group evaluations with regard to jaw treated as well as the attachment systems used showed that the frequency of complications did not change over time (P > .05). The differences detected were more matrix replacements after 5 years in the maxilla and mandible and more matrix replacements and patrix fractures after the first year in the mandible (P < .05). Among the attachment systems, a dislodged, worn, or loose matrix or its respective housing was more common in the ball-attachment group after the first year (P < .05). Prosthetic complications for all types of attachments were comparable (P > .05), except for the differences in peri-implant or interabutment mucosal enlargement rates after 1 year. CONCLUSIONS: Prosthetic maintenance requirements for overdentures on both jaws seem to be comparable. The impact of attachment system on the prosthetic outcome is negligible.

Marginal bone loss and prosthetic maintenance of bar-retained implant-supported overdentures: a prospective study.

PURPOSE: To compare marginal bone loss, soft tissue conditions, and prosthetic outcomes of implants supporting mandibular and maxillary bar-retained overdentures. MATERIALS AND METHODS: A total of 124 implants (80 in the mandible and 44 in the maxilla) were placed in 35 patients. Bar-retained overdentures were fabricated for each patient. Prosthetic complications were recorded throughout the study. Plaque, peri-implant inflammation, bleeding, and calculus indices were recorded, and standard periapical radiographs were obtained at each implant site for measurement of marginal bone loss. RESULTS: One implant failed in the mandible prior to prosthesis fabrication and one failed in the maxilla 5 years after prosthesis delivery. Both were replaced after 12 weeks of bone healing. The mean marginal bone loss around maxillary implants was greater than that around mandibular implants. Comparative evaluations of subgroups followed for < 5 years and greater than or equal to 5 years showed that soft tissue parameters were similar for maxillary and mandibular implants. One- and 5-year survival probabilities of the mandibular and maxillary overdentures were comparable. Kaplan-Meier and log-rank tests revealed that the probabilities of retightening of retainer and requirements for occlusal adjustments were higher for mandibular overdentures, whereas other maintenance requirements were comparable. The retainers in mandibular overdentures needed retightening more frequently than the retainers in maxillary overdentures. CONCLUSIONS: Dental implants supporting mandibular and maxillary bar-retained overdentures have similar peri-implant soft tissue outcomes and overall prosthetic survival probabilities.

Vascular smooth muscle contraction/relaxation of rat carotid artery is not altered by bone grafting substitutes in vitro.

PURPOSE: The aim of this study was to explore the effects of various bone grafting substitutes (Osteosponge, Perioglas, Tutoplast, and Surgibone) on vascular smooth muscle tonus. METHODS: Bilateral carotid arteries were removed from rats and contraction/relaxation of isolated vessel rings were measured before and after contact with the biomaterials and then, for dose-dependent epinephrine and papaverin administrations, by a force displacement transducer. The data of each biomaterial group were collected by a computerized system and corresponding software at a sample rate of 1,000 kHz and were converted to contraction force. RESULTS: Vascular contraction forces were influenced in response to biomaterials tested except for Osteosponge (P < 0.05), although the differences between groups were insignificant (P > 0.05). There was a dose-dependent vascular response to epinephrine and papaverine administration upon biomaterial contact (P < 0.05). The dose-dependent vascular responses to epinephrine and papaverine administration were almost similar for all biomaterials tested (P < 0.05), suggesting that the biomaterials led to reversible effects on vascular contraction/relaxation behavior, which resulted in recovery. CONCLUSIONS: Osteosponge, Perioglas, Tutoplast, and Surgibone do not alter vascular smooth muscle tonus and vitality and therefore would, presumably, not jeopardize the angiogenesis of fresh blood vessels and full vascularization during tissue healing.

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs.

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.