Photogrammetry--an alternative to conventional impressions in implant dentistry? A clinical pilot study

PURPOSE

The purpose of this clinical pilot study was to describe a photogrammetric technique to determine implant positions in the oral cavity, and to test and compare this technique to conventional impression/master cast procedures for fabrication of titanium frameworks with a computer numeric-controlled (CNC) milling technique.

MATERIALS AND METHODS

Implant positions were recorded by means of conventional impressions/master casts as well as intraoral 3-dimensional photogrammetric measurements in 2 patients who were provided with 5 Brånemark implants each in the edentulous mandible. For each patient 2 titanium frameworks were made by means of a CNC milling technique (All-in-One). Both frameworks had an identical design, but the orientations of the framework cylinder fit surfaces were machined either from measurements from the master casts or from the intraoral photogrammetric measurements. The frameworks were tried for fit in the oral cavity and on the master casts.

RESULTS

Both cases showed different precision of fit when comparing the 2 frameworks on the master casts. One of the 2 photogrammetric frameworks was not considered acceptable when tried on the models. In the oral cavity, however, all 4 frameworks presented comparable fit, and all were accepted for clinical use.

CONCLUSION

The clinical experiences with try-in of the 4 different frameworks indicated that the photogrammetric technique could be a valid option for conventional impressions when using CNC milling fabrication in implant dentistry. The different results from the model and oral examinations also imply the difficulties of assessing clinical fit when testing fit at the master cast level only.

[Development of partially sintered alumina block for dental CAD/CAM and mechanical properties testing]

OBJECTIVE

It is a new way to fabricate all ceramic crowns by combining dental CAD/CAM with glass infiltration technology.

METHODS

A partially alumina sintered block made of a high purity, fine alumina powder was shaped by isostastic pressure and sintered at 1,400 degrees C. Its mechanical properties were tested and microstructure was observed by SEM.

RESULTS

The Vicker's hardness, three-point bending strength, fracture toughness of partially sintered alumina block were 1.65 MPa, 210 MPa, 1.90 MPam1/2 respectively. Micrographs of SEM indicated that partially sintered alumina contained the structure of continuous three-dimensional open pores through the neck growth and surface diffusion of the interparticles.

CONCLUSION

The partially sintered alumina block that developed in this way may be used to mill for CAD/CAM and fabricate the shrinkage-free all ceramic crown.

All-ceramic posts and cores: the state of the art

Metal posts used to restore endodontically treated teeth may shine through all-ceramic crowns and thin gingival tissue. When nonprecious alloys are used, corrosion products may lead to discoloration. All-ceramic posts and cores can be used in combination with all-ceramic crowns to prevent these problems. All-ceramic posts and cores are highly biocompatible and will almost always increase the translucency of an all-ceramic restoration. The purpose of this article is to describe the fabrication of all-ceramic posts and cores, using high-toughness ceramic materials such as alumina or zirconia ceramics, through 4 different techniques: the slip-casting technique; the copy-milling technique; the 2-piece technique, which involves a prefabricated zirconia ceramic post and a copy-milled alumina or zirconia ceramic core; and the heat-press technique, which involves a prefabricated zirconia ceramic post and a heat-pressed glass-ceramic core. Indications, contraindications, advantages, and disadvantages of the different techniques are compared.

A screw lock for single-tooth implant superstructures

BACKGROUND

The most common complication in a single-tooth implant restoration is abutment screw loosening. Instability of the prosthetic superstructure is expressed by difficulty in chewing and functioning, as well as soft-tissue soreness and/or swelling that could lead to screw fracture. Manufacturers of oral implants have attempted to refine the connecting parts of the prosthesis to achieve a more predictable tightening method for the screws.

METHODS

To maintain the abutment screw tightly in its correct position, the authors developed a technique in which an elongated hexagonal titanium bar is inserted into the hexed fixed screw head. The screw is locked, and the bar is then fixed with a light-cured composite resin material that serves to seal the retaining screw access hole. The occlusal hexagonal bar thus serves as a secure screw lock that can be easily removed if needed.

RESULTS

The authors have used the hexagonal bar for almost three years on 120 single-tooth screw-retained prostheses in 100 patients (65 in the first and second premolar region, 40 in the incisor region and 15 in the posterior molar region). All of these prostheses functioned successfully, including those with wider occlusal planes and increasing occlusal forces. No screw loosening or fractures were noted in any of the fixtures.

CLINICAL IMPLICATIONS

This technique secures and stabilizes the single-tooth prosthesis, reduces chair time on follow-up procedures and reduces unnecessary frustration in patients and dental team members.

Diagnostic provisional restorations in restorative dentistry: the blueprint for success

There is no question that patients today demand a sophisticated level of restorative dentistry, in terms of both esthetics and function. No elective restorative dentistry should be undertaken without a clear understanding of the patient's expectations and the limitations of restorative therapy. The dentist should have a clear picture in mind of the final results before initiating irreversible therapy. The use of mounted diagnostic casts, diagnostic wax-ups and provisional restorations permits patient acceptance to be obtained before the definitive phase is initiated. Too often the dentist does not take advantage of this important restorative option, with disastrous results when definitive restorations are viewed by the patient for the first time. By following the plan of treatment outlined in this article, such disasters can be avoided.

Current status of ceramic coatings for dental implants

There are various ceramic coatings available for dental implants. From a commercial standpoint, plasma-sprayed hydroxyapatite (HA) is the most popular. These coatings are typically partially amorphous after processing and contain crystalline phases other than HA. Plasma-sprayed HA and the other bioactive ceramic coating materials have been shown to enhance bone apposition as compared with uncoated metal implants. Some of the other available materials include the bioglasses, other calcium phosphates such as fluorapatite and tricalcium phosphate, and the inert ceramics such as alumina. The plasma-spray process is not optimum for all types of ceramic coatings, because it is not suitable for coating porous surfaces; the exact control of structure and chemistry is difficult with this process, and bond strength is not as high as is desired for some applications. Alternative methods for coating include sol-gel processing, ion beam and radio frequency (RF) sputtering, pulsed laser deposition, hot isostatic pressing, and electrophoretic deposition. The use of osteoinductive agents in conjunction with ceramic-coated implants is of current interest, and the degree and type of bonding of these agents appear to vary with the composition of the ceramic coating. Because there seems to be no satisfactory means of incorporating osteoinductive agents into ceramic coatings during any of the conventional coating procedures, the best approach seems to be to diffuse the agents into the coating after processing. Other possibilities include the tethering of the agents to the surface of the ceramic by suitable organic molecules or the placing of the agent in some carrier material such as a cement, which is placed around the implants.

Compliant Keeper system replication of the periodontal ligament protective damping function for implants: part II

STATEMENT OF PROBLEM

There are numerous articles regarding implant overloading, interfacial integrity and component failure. A significant amount of literature review supports the concept of the progressive loading and damping, and it should be addressed.

PURPOSE

This study was designed to correlate durometer measurements of the elastomeric test materials and actual Periotest values (PTV) of the test materials as preloaded sleeve rings in Compliant Keeper abutments to support the Compliant Keeper as a viable implant damping system.

MATERIAL AND METHODS

A 4-unit fixed-removable implant-supported partial denture was the test model. Sleeve ring combinations replaced "O" rings and 220 Periotest measurements were graphically recorded, then analyzed by least square of means, 2-way analysis of variance, and a Tukey test.

RESULTS

There was a correlation between durometer measurements and PTVs of sleeve rings. Finite movement was measured accurately with the Periotest (P =. 0001) so that Compliant Keeper systems can be programmed to match the movement of another implant abutment, because they might be able to match the PTV of a natural abutment.

CONCLUSIONS

Significant differences exist between the "O" rings and sleeve rings. The sleeve ring, as a controllable damping element, enables the Compliant Keeper system to provide progressive loading and damping for implant-supported prostheses.

The effect of the use of a counter-torque device on the abutment-implant complex

STATEMENT OF PROBLEM

Little is known about the condition of the abutment-screw joint before loading, after the development of the preload.

PURPOSE

This study examined the tightening force transmitted to the implant with and without the use of a counter-torque device during the tightening of the abutment screw.

MATERIALS AND METHODS

Forty Brânemark implants and 10 CeraOne, Estheticone, Procera, and AurAdapt abutments formed the experimental populations. Samples in each group were further divided into 2 groups, 1 group was tightened with a torque controller without the use of a counter-torque device, whereas the other used the counter-torque device. Samples were positioned in a special holder within the grips of a Tohnichi BTG-6 torque gauge for measuring transmitted forces.

RESULTS

There were significant differences (P =. 0001) in the tightening forces transmitted to the implant with and without the use of a counter-torque device when tightening the abutment screws.

CONCLUSION

An average of 91% of the recommended preload tightening torque was transmitted to the implant-bone interface in the absence of a counter-torque device. In all abutment systems, less than 10% of the recommended preload tightening torque was transmitted to the implant when the counter-torque device was used.

Indexing procedures for converting removable partial dentures after extractions while the patient retains the prosthesis

A new indexing procedure is described for the conversion of removable partial dentures when extraction of additional teeth is planned. Advantages and disadvantages of the indexing procedure are reviewed and compared with traditional treatment options. The new procedure facilitates the use of dental laboratory expertise and facilities and allows the patient to retain the prosthesis throughout the process. A component that includes teeth, denture base segments, and wire or cast clasps is created by the laboratory and attached by the dentist during the extraction visit as a simple denture repair procedure. The procedure can also be used to convert an existing partial denture to an immediate complete denture. Required clinical and laboratory procedures are described.

[A biomechanical study of dental implants using a method for 3-dimensional volumetric mathematical modelling]

Biomechanics of the dental implants introduced into alveoli immediately after tooth extraction has been investigated. The programme ANSYS has been used. Three-dimension volume mathematical models were calculated, with the help of which the tense-deformed state of the supportive biological tissues has been investigated in the area of direct implantation. On the grounds of the results obtained a conclusion has been made that there is an essential improvement of the load distribution under investigation of the inner bone modified biologically designed implants for direct implantation.

Intracrown ring for crown and fixed partial denture abutments

When a tooth prepared for a crown does not comply with the general principles of retention and resistance form, and it is not possible to correct it without damage to the biologic structures of the tooth, consideration must be given to the purpose of the crown, such as whether it is a single crown, a retainer for a fixed restoration, or a retainer for a fixed removable prosthesis with precision attachments. The crown prepared with receptacles for internal attachments will undoubtedly require more retention and resistance to dislodgment than a single crown because of forces that will be applied to it through the removable portion of the restoration. The purpose of this article is to present an alternative procedure that uses the intracrown ring, which provides additional retention for the abutment crown because of the compressible ring. The compressible ring is placed in the groove prepared in the lower third of the abutment during the crown preparation.

[CAD/CAM-copings for partial coverage]

Aim of the study was to evaluate the Computer Integrated Ceramic Reconstruction (CICERO)-system and the Ceramic Reconstruction (CEREC)-system for the production of all ceramic copings for partial coverage. Posterior teeth were prepared and the stone dies were made. Accuracy analyses were performed on ceramic restorations made by means of the CICERO and by means of the CEREC technique. The marginal gaps were compared to that of a control cast metal restoration. The results demonstrate that the marginal gaps of the CICERO and CEREC copings varied respectively for the premolar 58-80 microns (mean 69 microns) and 71-91 microns (mean 81 microns). For the upper molar 63-92 microns (mean 78 microns) and 68-110 microns (mean 89 microns) and for the lower molar 54-98 microns (mean 76 microns) and 73-99 microns (mean 86 microns). Control cast metal partial coverage restorations showed marginal gaps of 33, 49 and 41 microns. It is concluded that computers can produce copings for partial coverage preparations on stone dies with a mean marginal gap for CICERO copings of 74 microns and for CEREC copings of 85 microns. These values were obtained before optimizing the marginal fit by means of porcelain veneering.

New techniques in spark erosion: the solution to an accurately fitting screw-retained implant restoration

How accurate is today's method of casting in the dental laboratory? Normally it is good enough, but what happens if the dental technician is confronted with an extensive restoration or has to deal with the precision of prefabricated implant abutments? In either case, he or she is headed for trouble. So what is to be done, especially if both of these components come together? The force transferred to the osseointegrated endosseous implants is naturally undesirable and the main reason for premature loss of the implants. The present article describes the production of an implant-related restoration for a 50-year-old patient. The plans were to make a partially removable, implant abutment-- connected, base metal framework and to administer spark-erosion machining to achieve a passive fit.

Computer-assisted design and manufacture of posterior full crowns

OBJECTIVE

To build an experimental system for the computer-assisted design (CAD) of full crowns and to obtain data for computer-assisted manufacturing (CAM) of full crowns.

MATERIALS AND METHODS

Three steps are involved in building the system: measuring the prepared tooth, the adjacent mesial and distal teeth, and the opposing teeth by means of digital speckle correlation; reconstructing the shape of the measured teeth; and developing CAD for full crowns. The standard shape of the corresponding tooth was modified to fit the defective tooth on the basis of buccolingual and occlusal-gingival distance as well as the occlusal relationship of the defective tooth.

RESULTS

CAD for full crowns was developed and was obtained for CAM of posterior full crowns.

CONCLUSIONS

The CAD method for full crowns is convenient and economical and can be used for anterior and posterior crown design, copying, and veneer.

Evaluation of visual and instrument shade matching

STATEMENT OF PROBLEM

Visual color matching to determine shades in dentistry is inconsistent and unreliable. If accurate, instrumental measurement of tooth color would provide objective, quantified data to match natural teeth to clinical shade guides.

PURPOSE

This study evaluated and compared the ability of a new computerized colorimeter and a simple visual test to match ceramic shade guide teeth.

MATERIAL AND METHODS

Thirty-one (n = 31) observers with normal color vision were allowed unlimited time to match one set of Vita Lumin shade guide teeth to the corresponding shade guide teeth of a second Vita Lumin shade guide. The same test was administered to 14 of the observers several months later to determine within-subject variability. A computerized colorimeter (Colortron II) equipped with a positioning guide was used to measure the middle third of each shade guide tooth. Through a "match tool" present in the computer's software, readings from one shade guide were matched with readings of the other shade guide by using CIELAB measurements and DeltaE values. The mean number of correct matches by the colorimeter and of correct matches in visual test were compared with a 1-tailed t test. Repeatability for both tests was determined with a paired t test.

RESULTS

The Colortron II instrument correctly matched 8 of the 16 tabs (50% correct), whereas visual matching by examiners averaged 7. 7 of 16 correct matches (48% correct) (standard deviation 2.7). No statistically significant differences existed between the 2 methods. The colorimeter demonstrated 100% repeatability and the visual test demonstrated fair repeatability (correlation coefficient r =.60).

CONCLUSIONS

Shade determination by visual means was inconsistent. Accuracy of a new colorimeter in matching porcelain shade guide teeth was only slightly better.

[The features of using intraosseous implants with intramobile elements]

Functional features of type Brånemark implants are compared with those of type IMZ implants. The problem of determining optimal stiffness characteristics of type IMZ implants has been solved by means of linear programming. The conclusion was made on considerable improvement in distribution of loads when type IMZ osseointegrated implants are used as supporting elements in the denture.

The effect of tooth preparation form on the fit of Procera copings

PURPOSE

This study evaluated the marginal and internal adaptation of Procera copings using different tooth preparations. The variations comprised 4 finish line forms, 3 occlusal forms, 3 occlusocervical undulation forms to the proximal finish line, and 3 proximal auxiliary retention forms.

MATERIALS AND METHODS

One hundred twenty preparations were made and copings were fabricated, cemented, embedded in an epoxy resin, sectioned, and measured at 14 sites.

RESULTS

The feather-edge finish line had the highest mean external marginal opening (135 +/- 79 microns), compared with the chamfer finish line (64 +/- 38 microns), the 0.8-mm rounded shoulder (51 +/- 34 microns), and the 0.5-mm rounded shoulder (68 +/- 56 microns). All 3 forms of occlusal reduction produced comparable internal adaptation at the axial wall. Specimens with normal occlusal reduction had the best occlusal adaptation at the cusp tip but not to a statistically different degree from the exaggerated form. Variations in the vertical height of interproximal finish lines did not significantly affect marginal opening. However, proximal retentive features less than 2.5 mm wide and more than 0.5 mm deep cannot be accurately reproduced with the present Procera scanner tip.

CONCLUSION

Feather-edge finish-line forms, deep retentive grooves, and deep occlusal morphology are not well reproduced using this system, but all other finish-line forms and design variations are accurately and clinically acceptably reproduced using this system.

Compliant Keeper system replication of the periodontal ligament protective damping function for implants: Part I

STATEMENT OF PROBLEM

Numerous reports and studies have been published relative to implant overloading, interfacial integrity, and component failure. A significant amount of literature review supports the concept of progressive loading and damping and that it should be addressed.

PURPOSE

This article reviews the literature on load reduction and uses the Periotest instrument to evaluate the viscoelastic materials of the Compliant Keeper implant damping system in vitro.

MATERIAL AND METHODS

The test model was a vice-mounted resin mandible replica with a 4-unit fixed-removable implant-supported Compliant Keeper partial denture. Pontics were both cantilevered and bounded. Three 13-gauge measurement extensions were located facially on the gingival, middle, and occlusal thirds of each abutment and pontic for 312 Periotest measurements of O-ring combinations with a titanium O-ring as the null control. Measurements were averaged and recorded.

RESULTS

Because the Periotest can measure finite movement below Miller Class I, Periotest values were obtained for O-rings so that they could be used to program a Compliant Keeper system to match the Periotest values of another implant body.

CONCLUSIONS

Significant loading differences were found with the O-rings. The O-rings controlled the damping element so they enabled the Compliant Keeper system to provide damping and progressive loading for implant-supported prostheses.

Comparison between freestanding and tooth-connected partially stabilized zirconia implants after two years' function in monkeys: a clinical and histologic study

STATEMENT OF PROBLEM

Partially stabilized zirconia implants placed by a 1-stage procedure have been previously shown to obtain initial osseointegration under clinically unloaded condition. However, it is unknown whether freestanding and tooth-connected partially stabilized zirconia implants can maintain a long-term direct bone-implant interface.

PURPOSE

This study examined the possibility of the long-term stability of osseointegration around partially stabilized zirconia implants with a 1-stage procedure with different loading designs.

MATERIAL AND METHODS

Thirty-two partially stabilized zirconia implants were placed into the mandibles of 8 monkeys. Three months after implant placement, 3 types of superstructure were provided in each animal to obtain different concepts of support as (1) single freestanding implant support, (2) connected freestanding implant support, and (3) a combination of implant and tooth support. At 12 and 24 months after loading, clinical, histologic, and histomorphometric evaluations of peri-implant tissues were performed on 28 implants.

RESULTS

No clear difference in clinical features was observed among the different types of support. Direct bone apposition to the implant was generally seen in all groups. Histometrically, bone contact ratio ranged between 66% and 81%, and bone area ratio varied between 49% and 78% at 24 months after loading. These values showed almost no difference among single freestanding, connected freestanding, and implant-tooth supports of partially stabilized zirconia implants.

CONCLUSION

In a primate model, partially stabilized zirconia implants placed with a 1-stage procedure achieve long-term stability of osseointegration with the use of single freestanding, connected freestanding, and implant-tooth supports.

Use of prosthesis-generated computed tomographic information for diagnostic and surgical treatment planning

Diagnosis, treatment planning, and prediction of a final implant-supported prosthetic outcome require precise noninvasive presurgical information. By combining the use of a clinically verified barium-coated template and interactive computed tomography (SIM/Plant, Columbia Scientific, Inc., Columbia, Maryland), the implant team can determine and address the relevant issues affecting treatment outcomes. Those issues include: implant-prosthesis incompatibility, recognition of anatomic limitations and anomalies, the need for presurgical bone augmentation, implant diameter and distribution, abutment type and angle, bone density, soft tissue augmentation requirements, accurate fee determination, and medicolegal protection. The data collection methodology and format for the Mecall and Rosenfeld prosthesis prediction analysis are discussed as part of case presentation.

Spark erosion for precise fitting of implant retained restorations

This article describes modern, precise methods of imaging and manufacturing implant-retained dental restorations. Scan data, combined with spark erosion technology, eliminates many of the problems associated with implant retained restorations.

Development and manufacture of prosthodontic components: do we need changes?

PURPOSE

Prosthodontic components for implant treatment have been developed with minimal reported scientific investigation. This paper aims to highlight a number of problems caused by this approach to the development and marketing of prosthodontic components and to suggest solutions.

CONCLUSION

Prosthodontic components must be developed with a scientific approach that involves both laboratory and clinical testing so as to optimize treatment outcomes in the future.

Electroforming technique

Electroforming technology is used to form substructures for porcelain inlays and crowns. This technique may be used as an alternative to the currently available porcelain-fused-to-metal and all-ceramic systems. Composed of pure 24 K gold deposited directly onto a duplicate die, electroformed copings are relatively thin (0.2 mm), highly biocompatible, and present a marginal accuracy of 20 microns on average. The equipment is relatively easy to use and therefore makes this technique attractive to small ceramics laboratories. The esthetic advantages of a gold colored substructure, the reduced thickness of the coping, and the improved fit of the gold collar when it is used, present a restorative alternative to the dentist, to the ceramist, and to the patient.

A method of making decalcifications in the porcelain build up

This article describes a method for making white decalcifications or modeling characterizations that attempt to duplicate natural teeth. Common techniques often use white stain applied to the wet porcelain or painted on as surface stain. A simplified and reproducible technique is provided that allows this characterization to be completed as part of the porcelain build up. A mixture of three powders causes an improved appearance that can lighten the incisal and occlusal surfaces to help create greater contrast with the body porcelain for a more natural result.

Helical CT scanning for CAD/CAM subperiosteal implant construction

Subperiosteal implant is the treatment of choice for the fully or partially edentulous atrophic mandible if grafting procedures are not contemplated to give the jaw sufficient available bone for endosseous implants. The main disadvantage of the standard technique for the construction of this implant is that it requires two surgical procedures. However, it is an accepted and proven technique with a long-term survival rate. This paper discusses the use of the CT scan subperiosteal implant, which provides a result similar to that of the standard subperiosteal implant, but requires only one surgical procedure. The accuracy of fit of the CT scan subperiosteal implant is similar to that of the implant fabricated by means of a standard two-surgical-impression technique. New updated CT scan machines use faster helical scanners and offer a great improvement over previous CT scan machines. The new CT scan machines reduce the chance of patient movement, produce a more accurate CT scan, and enable a more accurate model of the mandible or maxilla to be developed. This paper discusses the production of a well-fitting CT scan subperiosteal implant by a trained, knowledgeable, and cooperative team of dentist, CT scan technician, and radiologist, all of whom understand the technical means to achieve their goal.

Osseointegration for welded and cast prostheses: presentation of two cases

The author describes two cases of full dental arches with only a few natural teeth in place that were treated with multi-dimensional, osseointegrated implants. The former case utilized the technique of titanium casting of the caps on natural teeth and on implants, with intra-oral welding of the caps to the implants. In the latter case, the techniques of welding and casting differ.

A modified occlusal registration and implant transfer technique

The technique for the transfer of implant and abutment position to a working cast has been hindered by multiple transfers and record reproductions. These serve only to delay completion of the patient's prosthetic requirements. A transfer technique that uses custom impression trays fabricated from surgical templates allows for a single-visit transfer of centric occlusion, vertical dimension, tooth position, and implant or abutment location in one procedure. This streamlines treatment and allows for quicker delivery of final prostheses.

Radiographic inspection of dental castings

Underdimensioning may adversely affect the clinical use of a crown or bridge. Insufficient dimensions may be due to inadequate modelling or deficiencies caused by the casting process. The dimensions of cast objects are measured mechanically using a calliper. This method has often proved to be insufficient in detecting areas of too small dimensions. This paper presents a non-destructive method of inspecting dental castings using radiography. The occlusal thickness of a random sample of 150 crowns made during regular clinical treatment in our department was inspected mechanically and radiographically. We found that 19% of the crowns were only 0.1 mm thick or less at the thinnest spot, 18% were between 0.1 and 0.2 mm and 9% were between 0.2 and 0.3 mm. In comparison to mechanical examination, radiographic inspection usually showed smaller values.

Single implant tooth replacement

It has been shown that direct bone anchorage of dental implants will provide long-term predictability for single tooth implants and multi-unit implants. The function of implant-supported restoration is now routinely achieved. The real challenge facing the restorative dentist and laboratory technician is to achieve optimal aesthetics. The learning objective of this article is to review the prosthodontic procedures essential to maximizing natural aesthetics in implant supported restorations. It will provide a review of master impression techniques, prepable titanium abutments and designing the cement on restoration. Particular emphasis is directed to the soft tissue model from which a series of sequenced techniques can be followed to achieve optimal aesthetics. Analysis of the implant alignment with regard to the neighboring teeth will result in having to make a choice of which prepable abutment will maximize the aesthetic result. The following case outlines how to replace a single missing tooth using an externally hexed implant system and a prefabricated titanium abutment on a 26-year-old male patient.

[The enhancement of the efficacy of patient orthodontic treatment based on the mathematical modelling of prospective implant designs]

Opportunities to increase prosthetic treatment efficiency by means of applying osseointegrated implants of traditional and prospective types are analysed. A technique of mathematical modelling of the interaction between implants and jaw bone is exposed. The numerical model and applied program, developed on the basis of finite element method, enabling to analyse a stress strain state of the bone and to determine extreme safe loads on implants are described. It is shown, that the most loaded zone is a layer of the compact bone directly contiguous to the neck of the implant. That is in good agreement with the results of clinical research, according to which just this zone has the highest percentage of complications. Methods for further optimisation of implants and prosthetic structures for the purpose to perfect the techniques of prosthetic treatment are discussed.

Scanning electron microscopic evaluation of the effects of an air-abrasive system on dental implants: a comparative in vitro study between machined and plasma-sprayed titanium surfaces

An in vitro comparative study was conducted in order to evaluate the effects of an air-abrasive system on dental implant surfaces. Eight new titanium dental implants, four standard machined implants (machined group), and four standard plasma-sprayed implants (plasma-sprayed group) were selected for investigation. Both neck and body surfaces of the implants were analyzed. Each pair of implants in each group was treated as follows: the spray of the air-abrasive unit was applied to each area for 5 seconds on the first implant and 15 seconds on the second implant. A total of 24 areas were observed: 16 test implants and 8 controls. Scanning electron photomicrographs were analyzed by 3 examiners using a category rating scale (kappa = 0.594). The images were also computerized for texture analysis. The results indicate that a single air-powder abrasive treatment of the dental implants selected for this study modified their exposed surfaces. After treatment, the threaded neck surface of a machined group implant was least affected, whereas the body was the most altered. In the plasma-sprayed group, comparisons between implant surfaces showed little change. In the machined group, more change was observed in both neck and body areas. In all specimens, a 5-second exposure to the air-powder abrasive did not induce deep changes in the surfaces. A 15-second exposure modified all the specimen surfaces. Further studies are needed to evaluate the effect of these changes on the biological osseointegration process.

Prosthetic considerations in the fabrication of surgical stents for implant placement

The utilization of surgical stents/templates for implant placement is of significant importance to the success of the definitive prosthesis. However, major conceptual differences exist between surgical stents designed for implant-supported crowns and bridges and those designed for implant overdentures. In addition, various types of surgical stents exist within each group. In either case, optimizing the prosthetic result by customization of the stent should be a major consideration in the fabrication process. The design of the stent must account for several treatment conditions, including position of the implant, the tissue present, and the anticipated prosthesis. The teaching objective of this article is to present the prosthetic considerations in the fabrication and customization of surgical stents. The article compares the two groups and offers specific guidelines for the fabrication of surgical stents for the various types of restorations within each group.

Anatomically correct soft tissue profiles using fixed detachable provisional implant restorations

For the past decade, the dental profession has given very little thought to the design of fixed detachable restorations with anatomically correct emergence profiles. Over-contoured implant restorations are frequently seen, and they may be challenging for patients to maintain. This article will address the most common techniques used to improve the soft tissue profile, and will show how implant-borne provisional restorations allow ideal soft tissue profiles to be achieved.

Two-implant-supported single molar replacement: interdental space requirements and comparison to alternative options

Posterior single-tooth implant restorations are subjected to an increased risk of bending overload. A high incidence of implant fracture has been reported when using a single standard 3.75-mm-diameter implant to support a molar restoration. The purpose of this article is to demonstrate the clinical feasibility of placing two implants to support a molar restoration and to compare this treatment option to the use of a single standard implant or a wide-diameter implant. Two osseointegrated dental implants used to support a molar restoration in interdental spaces as small as 10 mm is shown to be effective and predictable in 60 restorations over the past 7 years. The use of two implants provides more surface area for osseointegration and spreads the occlusal loading forces out over a wider area, reducing the potential bending forces that would otherwise exist in a single-implant molar restoration.

A study on the grinding accuracy of a copy milling machine for dental use

In order to assess the relationship between the profiling pressure of a copy milling machine for dental use and the accuracy of the dimensions of the objects produced, a Celay System was used to profile a metal-cylinder model, and its dimensions were compared with the workpieces. The results showed that, when a cylindrical model with a diameter of 6 mm was subjected to freehand profiling, the mean processing error of the object produced was -0.026 mm, and the profiling pressure was 4.6 gf to 131.7 gf (mean: 76.6 gf). However, the fluctuations in profiling pressure decreased by 1/5 during profiling operations when accessories that fixed the profiling pressure and the profiling loci were used. Moreover, while the processing error when the model was profiled at a profiling pressure of 76 gf or less was a mere 0.005 mm, at 110 gf it rose to 0.022 mm. Based on the above, the processing error that occurred as a result of profiling pressure appeared to affect processing accuracy. On the basis of these findings, profiling as light weight must be performed with as possible in order to obtain accurate products using the copy milling machine for dental use, and the results suggested the necessity of attaching control devices to the copy milling machine to make accurate restorations.

Laboratory procedures for fabricating pressable all-ceramic restorations

Part 1 of this article covered the applications, preparation requirements, and procedures through divesting for the pressable ceramic system. The O.U. (opacity units) system was also described, and how it relates to the proper selection of core material.

Fit of veneers made by CAD-CAM and platinum foil methods

Veneers were fabricated by CEREC CAD-CAM and the platinum foil techniques for standardized preparations on 10 artificial teeth. Mesial preparation contacts were broken, but distal contacts remained intact. The veneers were cemented in a standardized manner to their teeth. The veneers and their attached cement were embedded in epoxy resin and sectioned twice gingivally-incisally and mesially-distally to produce eight sections. Three-way ANOVA disclosed that the main effects of fabrication method, section location, and measurement point location as well as all interaction terms significantly affected fit (P < 0.05). However, the difference in mean overall fit between the fabrication methods was too small to be of clinical importance. Restoration of the broken approximal contact did not compromise fit. Incisal margins had the greatest marginal openings. Surface measurement point locations were less well adapted than internal locations. Fit maps for CEREC and platinum foil veneers were strikingly similar.

Laboratory procedures for fabricating pressable all-ceramic restorations

All-ceramic restorations have been recognized and accepted as being esthetically superior to porcelain-fused-to-metal or all-cast restorations. However, gains in esthetics achieved with an all-ceramic crown often meant sacrifices in strength, fit or both. Recent developments in the pressed ceramic format continue to secure the pressed all-ceramic restoration as a viable alternative to porcelain-to-metal and all-cast restorations. This article focuses on the most updated techniques and considerations of this type of system and its effectiveness in providing esthetics, strength and fit through "technician-friendly" procedures, materials and equipment.

Finite element stress analysis of IMZ abutment designs: development of a model

PURPOSE

This article describes the development of a model system for use in finite element stress analysis of three different IMZ abutment designs: original threaded Intra-Mobile Element (IME), Abutment Complete (ABC), and Intra-Mobile Connector (IMC).

MATERIALS AND METHODS

A three-dimensional model simulating a cast gold crown restoration attached to an osseointegrated IMZ implant fixture was generated for each abutment design. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A convergence test was performed to optimize the mesh. Convergence test mesh refinement for the IME, the IMC, and the ABC abutment models resulted in 818 elements, 2,566 nodes; 738 elements, 2,362 nodes; and 663 elements, 2,051 nodes, respectively. Progressive tightening of the retaining screw (preload) was simulated; the degree of screw tightening necessary to prevent opening of the crown-abutment interface in extreme loading (500-N occlusal load at 45 degrees) was determined individually for each system.

CONCLUSIONS

Models of three IMZ abutment designs have been refined and the appropriate relative screw preloads determined. This model system is to be used subsequently in stress analysis comparison for the three systems.