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PubMed1997

Wear of visible light-cured restorative materials and removable partial denture direct retainers.

PURPOSE: This study measured the in vitro wear of visible light-cured restorative materials and removable partial denture direct retainers. MATERIALS AND METHODS: An aluminum test die was produced by replicating the facial contours of an extracted human molar (model). The replica's cervical contour was modified by placement of a restorable Class V cavity preparation. The test die became a fixed component of a testing apparatus. The restorative materials tested were Z100 (fine particle filled resin composite), Silux Plus (microfilled resin composite), and Photac-Fil (hybrid glass ionomer). Cast round, half round, I bar, and wrought-wire retainers were designed to engage a 0.254-mm undercut. Caliper measurements of the wear of restorative materials were made at intervals during testing, and after 7,500 retainer placements and removals. The measurements of material- and retainer-wear were subjected to ANOVA and Tukey tests. RESULTS: Generally, retainers with round profiles caused less wear of the restorative materials than those featuring flat contact surfaces. Wear of the materials ranged from 14 +/- 5.5 microns (Silux Plus by cast round) to 70 +/- 10.0 microns (Photac-Fil by cast half round). Mean wear of retainers, however, ranged only from 2 +/- 4.5 microns for six of 12 possible retainer-material pairings up to 12 +/- 4.5 microns (cast half round by Z100). CONCLUSIONS: Regardless of their design features, the direct retainers of this study exhibited little wear when paired with any of the restorative materials. Overall, material wear appeared to be greater than retainer wear by a factor of five. When paired with practically any retainer type, the hybrid glass ionomer (Photac-Fil) exhibited more wear than either of the two resin composites (Z100 or Silux Plus). Although not established clearly, retainers with round profiles (wrought-wire and cast round) appeared to produce less wear of restorative materials than their I bar and cast half round counterparts.

Analysis of Variance↗
PubMed1999

Compressive and tensile zones in the cement interface of full crowns: a technical note on the concept of resistance.

PURPOSE: The objectives of the study were: 1) to map the stresses acting on the cement interface of crown and abutment analogs during loading; and 2) to provide a theoretical basis for the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement lute. MATERIALS AND METHODS: Three-dimensional finite element (FE) meshes of crown and abutment analogs were constructed and loaded in a direction perpendicular to the axes of symmetry of the abutments. Three parameters were investigated: taper (10 degrees and 20 degrees of convergence), abutment substrate (Ni-Cr alloy and dentin), and type of cement (zinc oxide eugenol, zinc phosphate, glass ionomer, and composite resin). The tensile and compressive components of the resulting force systems were plotted along two axes (z: parallel to the axis of symmetry of the crown/abutment complex; and y: perpendicular to z, i.e., parallel to the direction of loading). Von Mises stresses were also generated. RESULTS: First, it was shown that the restoration's axis of rotation was located inside the abutment cone and was perpendicular to and intersected the axis of symmetry of the crown/abutment complex. Second, stress distribution was dependent on the three parameters investigated. Varying taper led to shifts due mainly to alterations in specimen geometry, whereas the abutment substrate and the cement type had a bearing on the level of the axis of rotation. The smaller the modulus of elasticity of the abutment substrate or the cement lute, the farther apical the location of the axis of rotation. CONCLUSIONS: Conventional schemes for explaining crown dislodgment in which the restoration rotates around an axis located at the preparation margin should be reassessed. The results of the FE analysis are compatible with the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement interface.

Chromium Alloys↗
PubMed2004

Crowns cemented on crown preparations lacking geometric resistance form. Part II: effect of cement.

PURPOSE: This study evaluated the effect of different cements on resistance to dislodgment of crowns cemented on preparations lacking geometric resistance form. MATERIALS AND METHODS: A preparation that offered no geometric resistance form, with 20 degrees total occlusal convergence (TOC), 0.9 mm wide shoulder finish line, and a 2.5 mm axial wall height was created on an ivorine tooth using a milling machine. Ten metal test specimen die replicas and 10 standardized metal crowns with recipient sites for the application of external forces through a universal testing machine were fabricated. The crowns were cemented on the dies under 5 and 10 kg external loads, the marginal openings measured, loaded to dislodgment, and cleaned of cement. The process was repeated using zinc oxide and eugenol (ZOE), zinc phosphate (ZPh), resin modified glass ionomer (RMGI), and composite resin (CR) cements. RESULTS: Marginal openings under 5 kg cementation loads were 74.63 (+/-15.04) for ZOE, 75.98 (+/-18.20) microm for ZPh, 98.58 (+/-22.62) microm for RMGI, and 105.82 (+/-20.07) microm for CR cements respectively; under 10 kg cementation loads they were 57.62 (+/-15.86) microm, 59.55 (+/-15.41) microm, 95.00 (+/-19.52) microm, 101.30 (+/-12.52) microm respectively. Oblique dislodgment forces, measured with a Universal testing machine, were 40.18 (+/- 6.76) N for ZOE, 215.65 (+/-45.79) N for ZPh, 165.43 (+/-19.53) N for RMGI, and 181.54 (+/-30.75) N for CR respectively when crowns were cemented under 5 kg loads. The corresponding values for 10 kg loads were 38.62 (+/-4.19), 274.86 (+/-54.22), 139.70 (+/-21.71), and 160.40 (+/-21.21) respectively. Only zinc phosphate cement produced statistically enhanced resistance when crowns were cemented under 10 kg force (p value = 0.035). CONCLUSIONS: Under the conditions of the present study only crowns cemented with zinc phosphate displayed increased resistance to dislodgment on preparations lacking resistance form.

Cementation↗
PubMed2004

Microbiological and clinical effects of chlorhexidine enclosed in fixtures of 3I-Titamed implants.

This double-blind study used a split-mouth design to investigate the microbiological and clinical effects of 0.2% chlorhexidine enclosed in fixtures. Twelve patients had 46 fixtures implanted. At second-stage surgery, a microbiological sample (baseline sample) of the inner parts of the fixtures was taken. Then, a 0.2% chlorhexidine solution was applied into the inner space of 23 fixtures (test group), and in 23 fixtures saline was applied (control group). Abutments were installed and gingival index, plaque index and crevicular fluid flow were monitored weekly. After 6 weeks, a second microbiological sample of the inner part of the fixtures was taken. At baseline, viable bacteria were detected within 46% of the fixtures. After weeks, bacteria were found in 87% of the fixtures. The numbers of bacteria in the control group were significantly higher than those in the test group. The results indicate that, after first-stage surgery, contamination of the inner spaces of the fixtures is commonplace. Application of a 0.2% chlorhexidine solution at second-stage surgery inhibits growth or acquisition of bacteria in the fixtures. In both test and control groups, the crevicular fluid flow as well as the gingival index decreased during the experimental period. At 4, 5, and 6 weeks after chlorhexidine application, these values in the test group appeared lower, but did not attain statistical significance.

Anti-Infective Agents, Local↗
PubMed2004

Implant design and interface force transfer. A photoelastic and strain-gauge analysis.

OBJECTIVES: To compare stress and strain magnitudes of butt-joint and internal-cone oral implants in a bone simulant. MATERIAL AND METHODS: Photoelastic and strain-gauged models of solitary Brånemark, ITI and Astra Tech implants were obtained. Vertical and 20 degrees oblique forces of 100 and 150 N were applied on the abutments in separate load cases. Isochromatic fringe patterns around implants were observed and photographed in the field of a polariscope. Strain-gauge measurements were performed and principal strains induced around implants were calculated. RESULTS: Isochromatic fringe orders of all designs were similar under both loading conditions (P>0.05). Strains around Brånemark implants were lower than around Astra Tech and ITI implants, particularly under vertical loads. The latter implants had similar strain magnitudes (P>0.05), although strains around the conical Astra Tech implant were lower under vertical load. CONCLUSIONS: Butt-joint and internal-cone oral implants have similar force distribution characteristics. The implant-abutment mating design is not a decisive factor affecting stress and strain magnitudes in a bone simulant.

Biomechanical Phenomena↗
PubMed2004

Effect of implant design on survival and success rates of titanium oral implants: a 10-year prospective cohort study of the ITI Dental Implant System.

AIM: The aim of this 10-year study (observation time 8-12 years, mean: 10 years) was to compare the survival rates, success rates and incidences of biological complications using three different implant designs of the ITI Dental Implant System. MATERIAL AND METHODS: In 89 dental patients treated comprehensively, a total of 112 hollow screw (HS), 49 hollow cylinder (HC) and 18 angulated hollow cylinder (AHC) implants were installed depending on the available bone volume and according to prosthetic needs. One and 10 years after surgical placement, clinical and radiographic parameters were assessed. The incidences of peri-implantitis according to various thresholds were registered over 10 years of maintenance. RESULTS: Success criteria at 10 years were set at: pocket probing depth (PPD)< or =5 mm, bleeding on probing (BoP)-, bone loss < 0.2 mm annually. The survival rate for HS was 95.4%, for HC 85.7% and for AHC 91.7%. Ninety percent of all the HS, 71% of the HC and 88% of the AHC did not present with an incidence of peri-implantitis over the 10 years, HC having significantly higher incidence of peri-implantitis than HS (P< 0.004). With the success criteria set above, a success rate for HS of 74%, for HC of 63% and for AHC of 61% was identified at 10 years. However, including a definition of PPD< or =6 mm, BoP - and bone loss < 0.2 mm annually for success, the rates for HS were 78%, for HC 65% and for AHC 67%, respectively. Basing success criteria purely on clinical parameters (without radiographic analysis), such as: PPD< or =5 mm and BoP-, the success rates increased to 90%, 76% and 89%, respectively. With PPD< or =6 mm and BoP - as success criteria chosen, the respective rates were 94%, 82% and 94% for HS, HC and AHC implants, respectively. CONCLUSIONS: A significantly higher survival rate as well as a significantly lower incidence of peri-implantitis was identified for hollow screw design ITI Dental Implants after 10 years of service when compared to hollow cylinder design ITI Dental Implants (95.4% vs. 85.7%; 10% vs. 29%). Depending on the setting of the threshold criteria for success, success rates are highly variable and hence, reporting of success rates with elaboration on the criteria set appears crucial for comparison of different studies.

Adult↗
PubMed2004

Astra Tech and Brånemark system implants: a 5-year prospective study of marginal bone reactions.

This paper describes the 5-year results of a comparative study between Astra Tech and Brånemark system implants. The aim was to compare the systems primarily with regard to bone level changes, and also with regard to other variables of interest. Sixty-six patients with edentulous jaws were included in the study. Randomisation schedules were used to allocate the patients to the two implant systems. 184 Astra Tech implants with a titanium-blasted surface and 187 Brånemark implants with a turned surface were used. The implants were inserted with a two-stage technique and the insertion followed the routines for the respective implant system. All patients were provided with full-arch fixed bridges. All patients were followed up with clinical and radiographic examinations from fixture insertion to the 5-year follow-up. The total mean bone level change in the upper jaw between fixture insertion and the 5-year examination was -1.74+/-0.45 mm at the Astra implants and -1.98+/-0.21 at the Brånemark implants. The corresponding values for the lower jaw were -1.06+/-0.19 for Astra and -1.38+/-0.17 for Brånemark. The major postoperative changes of the marginal bone level took place between fixture insertion and baseline. During this period, there was also a different pattern of bone remodelling between the implant systems. Between baseline (prosthesis connection) and the 5-year examination, the marginal bone level changes were small, with no difference between the implant systems. The implant stability was examined with the supraconstructions removed. At the 5-year examination, the survival rate for Astra Tech implants was 98.4% and for the Brånemark implants it was 94.6%. The difference was not statistically significant.

Adult↗
PubMed2004

Influence of implant taper on the primary and secondary stability of osseointegrated titanium implants.

OBJECTIVES: The study presented was designed to analyse the mechanical performance and the primary and secondary stability characteristics of endosseous titanium implants with 1 degree (EXP1) and 2 degrees (EXP2) of taper when compared with the standard Brånemark design (Nobel Biocare AB, Gothenburg, Sweden). MATERIALS AND METHODS: One pair of 10 mm EXP1 and control implants were placed in the femoral condyles of six rabbits. Paired 6 mm EXP1 and control implants and 6 mm EXP2 and control implants were placed in the tibial metaphysis. The control implants used were 4 mm diameter standard Brånemark implants, the same length as the test implants. At placement, insertion torque (IT) and resonance frequency analysis (RFA) measurements were performed. Six weeks postoperatively when the animals were killed, RFA and removal torque (RT) measurements were made. RESULTS: At placement, significantly higher IT was needed to insert the EXP implants compared with the controls. RFA values were significantly higher for EXP1 implants placed in the tibia but not in the femur. In pooling data from the femur and tibia there was a significant difference. The EXP2 implants failed to insert fully and demonstrated a lower RFA value than may have been expected due to the exposed threads, although this difference was not statistically significant. CONCLUSIONS: The results from the present study showed that 1 degrees of taper results in a better primary stability compared with the standard Brånemark design. There was no evidence that the tapered design caused negative bone tissue reactions. All the implants gained in stability during the healing period.

Animals↗
PubMed2005

A novel computational method for real-time preoperative assessment of primary dental implant stability.

A novel methodology which allows for fast and fully automatic structural analysis during preoperative planning for dental implant surgery is presented. This method integrates a fully automatic fast finite element solver within the framework of new concepts in computer-assisted preoperative planning for implant surgery. The planning system including optimized structural planning was validated by experimental results. Nine implants were placed in pig mandibles and mechanically loaded using a testing rig. The resulting displacements were measured and compared with those predicted by numerical analysis during planning. The results show that there were no statistically significant differences (P = 0.65) between the results of the models and the experiments. The results show that fast structural analysis can be integrated with surgical planning software allowing the initial axial implant stability to be predicted in real time during planning. It is believed that such a system could be used to select patients for immediate implant loading and, when further developed, be useful in other areas of preoperative surgical planning.

Animals↗
PubMed2005

Biological and biomechanical evaluation of bone remodelling and implant stability after using an osteotome technique.

The influence of the osteotome technique on the osseointegration and biomechanical behaviour of cylinder implants (SLA, ITI was compared with conventional preparation of the implant site in an animal model. A total of 56 implants were placed in the cranial and caudal tibia condyle of six Gottinger minipigs. The implant site was prepared either by the conventional technique with drills (control group A) or by the osteotome technique (experimental group B). Resonance frequency measurements (RFMs) were made on each implant at the time of fixture placement and at the time of scarification. Half of the minipigs were sacrificed 7 days and 28 days after implant placement and the implants were removed with the surrounding bone. Bone tissue responses were evaluated by histological analysis and removal torque testing. For histological evaluation 30-50 microm-thick ground sections were examined. Biomechanical testing revealed a significantly higher stability of implants in the control group (A) than in the experimental group (B) (P = 0.004) at day 7. After 28 days implant stability in the control group remained significant higher (47%) than those of group B (P > 0.001). RFM demonstrated no significant difference between both groups and during the experimental course. Histological analysis demonstrated fractured trabeculae in peri-implant bone in the experimental group at day 7, while they were not posed at day 28. We conclude that the decreased implant stability by using the osteotome technique is based on microfractures in peri-implant bone.

Animals↗
PubMed2005

Positive effect of early loading on implant stability in the bi-cortical guinea-pig model.

Loading, early after implant placement, has gained rapid interest in dentistry. Primary implant stability, as e.g. defined by resonance frequency instrumentation, has been isolated as a predicator when immediate and early implant loading is applied. The aim of this study was to investigate the effect of early (after 7 days) mechanical loading on the establishment of osseointegration by means of resonance frequency analysis (RFA). Percutaneous titanium implants were installed in both tibiae of 10 guinea-pigs. One week after implant installation, one implant (test) was loaded daily for 6 weeks, while the contra-lateral served as the unloaded one (control). A sinusoidally varying bending moment was applied at a frequency of 3 Hz and a force amplitude of 5 N, for 1800 cycli. Resonance frequency was measured at implant installation and from then on weekly using the RFA-device (Osstell). Contrary to control implants, that showed a decrease in stability 1 week after installation, reaching a minimum at 3 weeks (-200 Hz), test implants showed a progressive increase in stability over time. After 6 weeks, the mean resonance frequency of test and control implants reached the same values. As confirmed by recent literature, early loading does not have to endanger the establishment of osseointegration of titanium implants. On the contrary, controlled loading is beneficial to maintain the implant stability during the early critical healing period as determined by RFA-measurements.

Animals↗
PubMed2005

The effect of platelet-rich plasma upon implant stability measured by resonance frequency analysis in the lower anterior mandibles.

Using a one-stage surgical protocol, a total of 34 Brånemark Mk-III Ti-Unite implants with a length of 13 mm and a diameter of 3.75 mm were inserted in 10 edentulous mandibles. Of these, seven patients received four and three patients two interforaminal implants. All implants were followed with repeated stability measurements by means of resonance frequency analysis at different time interval: 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44 days. In quadrant III platelet-rich plasma (PRP) was instilled locally before implant placement, while no PRP was added in quadrant IV to serve as control group (split-mouth design). Results showed no statistically significant difference between the two groups. Nonetheless, both groups (PRP+control) showed a highly significant reduction of the implant stability quotient (P<0.001) between days 0 and 4. However, no difference was noted between the two groups after day 4, it may be concluded that the instillation of PRP during implant placement in the lower anterior mandible did not add additional benefit.

Aged↗
PubMed2006

Analysis of bone-implant interaction phenomena by using a numerical approach.

OBJECTIVES: The purpose of the present work is to investigate the interaction phenomena occurring between endosseus dental implants and peri-implant bone tissue. MATERIAL AND METHODS: Detailed finite element models are adopted in order to analyze the actual behavior of bone-implant system depending on implant and anatomical site configuration and loading conditions. Different types of titanium dental implants are considered. Implant finite element models are obtained through a reverse engineering procedure and adopting specific software for the reconstruction of geometrical configuration. Anatomical sites are modeled starting from computerized tomography data, according to specific image processing procedures. RESULTS: Occlusal static forces are applied to the implants and their effects on the bone-implant interface region are evaluated. The influence of several parameters, such as morphometry of anatomical site or loading condition, on the biomechanical response of bone-implant system is considered. CONCLUSIONS: The evaluation of the biomechanical response of implant-bone compound necessarily requires the adoption of accurate numerical models, accounting for the complex geometry of threaded implants, as well as of the anatomy of the patients to be able to provide for reliable results pertaining to stress/strain path on peri-implant bone tissue.

Alveolar Process↗
PubMed2006

Resonance frequency analysis and damping capacity assessment. Part I: an in vitro study on measurement reliability and a method of comparison in the determination of primary dental implant stability.

OBJECTIVES: The aims of this in vitro study were to evaluate reliability of the Osstell and Periotest devices in the assessment of implant stability and to perform a method comparison. MATERIAL AND METHODS: Commercial dental implants were inserted into bovine rib segments of different anatomical origins and densities. Repeated measurements were performed, varying (a) the torque-in force of the devices' attachment screw (the Osstell transducer and the ball attachment, insert for the Periotest device), (b) the insertion site bone quality, and (c) the thread exposure in simulated peri-implant bone defects. RESULTS: Both methods were comparably reliable and showed a strong association to each other in the classification of implant stability. As opposed to torque-forced screw attachment, the variations in bone composition, differences in inter-implant stability of adjacent implants, and peri-implant bone reduction were statistically significant for both methods. CONCLUSIONS: Both non-invasive diagnostic devices seem to be useful in the long-term follow-up of implant integration.

Animals↗
PubMed2006

Resonance frequency analysis and damping capacity assessment. Part 2: peri-implant bone loss follow-up. An in vitro study with the Periotest and Osstell instruments.

OBJECTIVE: We compared the performance of damping capacity assessment (Periotest device) to resonance frequency analysis (Osstell device) in the assessment of peri-implant bone loss in an in vitro experiment. MATERIAL AND METHODS: Screw-type oral implants were polymerized into acrylic blocks. Peri-implant bone loss was simulated by successively removing defined portions of material surrounding the implants in millimeter increments. Measurement values of both devices were compared by assessing the associated measurement errors, by calculating correlation analyses and drawing scatterplots, and by means of regression analysis referring to increasing bone loss. RESULTS: Both devices produced comparable results suggesting agreement of the measured implant stability values to the actual loss of peri-implant resin. There was a noticeable correlation of the Periotest and Osstell implant stability values. CONCLUSION: The results of this experiment suggest agreement in predicting the actual implant stability with both the instruments with the Osstell instrument being the more precise device.

Acrylic Resins↗
PubMed2006

The effects of implant surface roughness and surgical technique on implant fixation in an in vitro model.

OBJECTIVES: The aim of the present study was to determine the relationship between implant surface parameters, surgical approach and initial implant fixation. MATERIAL AND METHODS: Sixty tapered, conical, screw-shaped implants with machined or etched surface topography were implanted into the explanted femoral condyle of goats. The implant sites were prepared either by a conventional technique, by undersized preparation, or by the osteotome technique. Peak insertion & removal torque, bone-to-implant contacts (BIC) and morphological bone appearance were assessed by scanning electron microscope (SEM) and micro-computer tomography. (micro-CT). RESULTS: Insertion and removal torque values were significantly higher for etched implants inserted with the undersized technique (115.2 +/- 31.1, 102.9 +/- 36.4 N cm) respectively. Also, the average BIC value was higher for the etched implants placed with the undersized technique (87.5 +/- 5.6), which was statistically significant compared with machined and etched implants inserted by conventional technique. CONCLUSION: In conclusion, this study shows that the surgical technique has a decisive effect on implant fixation (represented in this study by installation torque value/removal torque value and histomorphometric evaluation) in trabecular bone. Nevertheless, additional in vivo studies have to be done to prove the importance of surgical protocol for the final implant-bone response.

Animals↗
PubMed2006

Peri-implant soft-tissue health surrounding cement- and screw-retained implant restorations: a multi-center, 3-year prospective study.

OBJECTIVE: The purpose of this prospective clinical study was to evaluate peri-implant soft-tissue conditions and esthetic fulfillment during a 3-year follow-up period following prosthetic rehabilitation. MATERIAL AND METHODS: As part of a prospective multi-center study, 152 ITI dental implants were placed in 80 patients in the maxillary anterior region. Fifty-nine crowns (38.82%) were cement retained, while 93 (61.18%) crowns were screw retained. At loading and 3, 6, 12 and 36 months post-loading, modified plaque index (MPI), sulcus bleeding index (SBI), keratinized mucosa (KM), gingival level (GL), and esthetic fulfillment were recorded. RESULTS: All patients completed the study and no complications were reported. While statistically not significant at all time points, cement-retained crowns seemed to present a worsening trend in MPI and SBI scores. Interestingly, screw-retained crowns seemed to present an opposite picture, their MPI and SBI scores improved over time. While plaque accumulation, prophylaxis and depth of crown margin significantly affected levels of sulcus bleeding, prophylaxis alone played a key role in reducing plaque accumulation. No soft tissue recession was observed in either cement- or screw-retained crowns up to 3 years post-loading. Esthetic fulfillment survey revealed that patients did not have a preference for crown types; however, dentists favored cement-retained over screw-retained crowns. CONCLUSIONS: Peri-implant soft tissues responded more favorably to screw-retained crowns when compared with cement-retained crowns. However, no soft-tissue recession was observed in either type of crowns. Cement-retained crowns were preferred by dentists, while patients were equally satisfied with either type of crowns they received.

Crowns↗