Oral rehabilitation of maxilla: technical consideration

Oral rehabilitation of edentulous maxilla is particularly difficult because of the lack of bone in correspondence of maxillary sinuses, therefore, the surgeon is forced to place implants in sites where bone is more prevalent. In addition, patients require more frequent oral immediate rehabilitation in order to reduce the discomfort related to wearing a total denture. A viable solution to provide stability and retention of the prosthesis in a short time is represented by the technique of intraoral welding supporting total denture or fixed prosthesis. This goal may be achieved thanks to the technique of welding titanium bars onto implant abutments. In fact, the procedure can be performed directly in the mouth, eliminating the possibility of errors or distortions due to prosthetic procedures. This paper describes a case report and the most recent data regarding long-term success and high predictability of intraorally-welded titanium bar in immediate loading implants.

Effect of Nd:YAG laser parameters on the penetration depth of a representative Ni-Cr dental casting alloy

The effects of voltage and laser beam (spot) diameter on the penetration depth during laser beam welding in a representative nickel-chromium (Ni-Cr) dental alloy were the subject of this study. The cast alloy specimens were butted against each other and laser welded at their interface using various voltages (160-390 V) and spot diameters (0.2-1.8 mm) and a constant pulse duration of 10 ms. After welding, the laser beam penetration depths in the alloy were measured. The results were plotted and were statistically analyzed with a two-way ANOVA, employing voltage and spot diameter as the discriminating variables and using Holm-Sidak post hoc method (a = 0.05). The maximum penetration depth was 4.7 mm. The penetration depth increased as the spot diameter decreased at a fixed voltage and increased as the voltage increased at a fixed spot diameter. Varying the parameters of voltage and laser spot diameter significantly affected the depth of penetration of the dental cast Ni-Cr alloy. The penetration depth of laser-welded Ni-Cr dental alloys can be accurately adjusted based on the aforementioned results, leading to successfully joined/repaired dental restorations, saving manufacturing time, reducing final cost, and enhancing the longevity of dental prostheses.

Retention systems for implant-retained overdentures

There have been demographic and cultural changes in the past few decades with regards to edentulism. Conventional mucosa-borne dentures can be poorly accepted by some patients. Implant overdentures have a useful role to play in the treatment of some of these patients. Some form of attachment mechanism between the implants and the prosthesis is normally required. This paper updates the reader on the different types of attachment systems and bars available.

CLINICAL RELEVANCE

It is important that dentists and technicians are able to understand the advantages and disadvantages of different attachment types for overdentures, in order to select the most appropriate technique for each patient.

The effect of axial and oblique loading on the micromovement of dental implants

PURPOSE

To quantify implant displacement upon axial and oblique force application and compare the effects of bone quality using an in vitro experimental setup.

MATERIALS AND METHODS

One hundred ninety-two implants were inserted into artificial bone block specimens using a drill guide. Ninety-six implants were placed in soft cancellous bone and loaded in 10-N increments up to 80 N in axial and oblique (30-degree angle) directions (n = 48 in each group). The other 96 implants were inserted in dense artificial bone and loaded in axial and oblique directions in the same force increments. Three-dimensional displacement data were recorded for all implants using a noncontact optical image correlation technique based on photogrammetric principles, and the absolute displacement vector was calculated.

RESULTS

There were significant differences in the absolute implant displacement in the different bone densities over all load increments. Implant displacement was significantly higher in soft cancellous bone than in dense bone. Axial and oblique loading revealed significant differences in implant displacement in the cancellous specimens, whereas oblique loading showed increased displacement (339 ± 47 Μm at 80 N) compared to axial loading (266 ± 39 Μm at 80 N). However, axial and oblique loading showed no significant differences over all load increments when implants were inserted in dense specimens (absolute displacement with an 80-N load: 147 ± 10 Μm axial and 126 ± 17 Μm oblique).

CONCLUSIONS

Bone density influenced implant displacement. The loading character (axial versus oblique) significantly influenced implant displacement in soft cancellous bone block specimens only. However, the limitation of the measured displacement values to an in vitro application that did not represent the complexity of vital bone has to be considered.

[Clinical analysis of laser welding on porcelain bonded metal surface]

PURPOSE

To evaluate the clinical effect of laser-welded crowns and bridges.

METHODS

Two hundred defective crowns and bridges were welded by using Heraplus laser welding machine, and then restored by porcelain.

RESULTS

After being welded ,those defective crowns and bridges of different materials fit well and their marginal areas were also satisfactory. During the follow up period of one year, no fractured porcelain and crack were found at welding spots.

CONCLUSIONS

The technology of laser welding has no direct effect on welding spots between metal and porcelain and could be used to deal with the usual problems of the crowns and bridges.

Are sectioning and soldering of short-span implant-supported prostheses necessary procedures?

The aim of this study was to evaluate the fit between dental abutments and the metal framework of a 3-unit fixed prosthesis screwed to two implants to determine whether sectioning and soldering of the framework are in fact necessary procedures. The study was based on a model of a metal framework of a 3-unit prosthesis screwed to two implants. A total of 18 metal frameworks were constructed and divided into 3 groups: (1) NS group - each framework was cast in one piece and not sectioned; (2) CS group - the components of each sectioned framework were joined by conventional soldering; and (3) LW group - the components of each sectioned framework were joined by laser welding. The control group consisted of six silver-palladium alloy copings that were not cast together. Two analyses were mperformed: in the first analysis, the framework was screwed only to the first abutment, and in the second analysis, the framework was screwed to both abutments. The prosthetic fit was assessed at a single point using a measuring microscope (Measurescope, Nikon, Japan) and the marginal gap was measured in micrometers. Statistical analysis was performed using analysis of variance (ANOVA), Scheffe's test, Student's t-test, and Mann-Whitney U test. The NS group had larger marginal gaps than the other groups (p<0.01), while the CS and LW groups had a similar degree of misfit with no significant difference between them. The results revealed that, in the case of short-span 3-unit fixed prostheses, the framework should be sectioned and soldered or welded to prevent or reduce marginal gaps between the metal framework and dental abutments.

[Study of physical-mechanic characteristics of prosthetic construction after their adjustment with the use of laser welding and hot metal adding]

Study of physical-mechanic characteristics of connecting joints of beam construction after laser welding and hot metal adding was performed. Increase of microhardness of joints as well as small reduction of bending strength of prosthetic constructions was established.

Strength of attachment between band and glass ionomer cement

AIM

To determine the strength of attachment between plain stainless steel band material and glass ionomer cement.

METHODS

Seventy-five extracted upper premolars, free of visible structural defects, were used. The teeth were divided randomly into three groups and embedded in acrylic resin blocks. A short length of plain, stainless steel band material with a welded stainless steel standard edgewise 0.022 inch bracket was adapted to the buccal surface of each tooth. The bracket-stainless steel pads were then cemented to the teeth with either Bandtite (Group 1), Granitec (Group 2) or Ariadent (Group 3) glass ionomer cement and stored in an incubator at 37 degrees C for 30 days. The shear bond strengths of the specimens were measured and compared.

RESULTS

The mean shear bond strengths (SBS) were significantly different: Bandtite 0.7331 +/- 0.056 Mpa; Granitec 0.3869 +/- 0.047 Mpa; Ariadent 0.2931 +/- 0.033 Mpa (ANOVA, p < 0.001). Tukey HSD post-hoc tests also showed significant differences between Bandtite and Granitec, Bandtite and Ariadent, and Granitec and Ariadent (p < 0.001). All specimens failed at the band-cement interface.

CONCLUSION

The highest and lowest SBS were related to Bandtite and Ariadent cements, respectively. All cements had bond strengths less than the range of bond strengths considered to be clinically acceptable for bonded orthodontic attachments. Mechanical factors are important for band retention.

Evaluation of shear bond strength of porcelain bonded to laser welded titanium surface and determination of mode of bond failure

The aim of this study was to evaluate the shear bond strength of porcelain to laser welded titanium surface and to determine the mode of bond failure through scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS). Forty five cast rectangular titanium specimens with the dimension of 10 mm x 8 mm x 1 mm were tested. Thirty specimens had a perforation of 2 mm diameter in the centre. These were randomly divided into Group A and B. The perforations in the Group B specimens were repaired by laser welding using Cp Grade II titanium wire. The remaining 15 specimens were taken as control group. All the test specimens were layered with low fusing porcelain and tested for shear bond strength. The debonded specimens were subjected to SEM and EDS. Data were analysed with 1-way analysis of variance and Student's t-test for comparison among the different groups. One-way analysis of variance (ANOVA) showed no statistically significant difference in shear bond strength values at a 5% level of confidence. The mean shear bond strength values for control group, Group A and B was 8.4 +/- 0.5 Mpa, 8.1 +/- 0.4 Mpa and 8.3 +/- 0.3 Mpa respectively. SEM/EDS analysis of the specimens showed mixed and cohesive type of bond failure. Within the limitations of the study laser welding did not have any effect on the shear bond strength of porcelain bonded to titanium.

Magnet-retained implant-supported overdentures: review and 1-year clinical report

Open-field aluminum-nickle-cobalt magnets have been used in prosthodontics for many years, but success has been limited because these magnets are susceptible to corrosion by the saliva and because their retentive force is weak relative to the initial retention offered by mechanical attachments. More recently, magnets have been made from alloys of the rare earth elements samarium and neodymium, which provide stronger magnetic force per unit size. In addition, a new generation of laser-welded containers has improved protection from salivary corrosion. The current resurgence of interest in this type of attachment appears justified because, unlike mechanical attachments, magnets have potential for unlimited durability and might therefore be superior to mechanical ball or bar attachments for the retention of removable prostheses on implants. To date, no long-term prospective trials have been conducted to confirm the clinical durability of this new generation of magnets for retaining dentures on either teeth or implants. The aim of this study was to document initial clinical experiences and levels of satisfaction among edentulous patients treated with mandibular implant-supported overdentures retained using a new generation of rare-earth magnetic attachments. At the outset, all but one of the 17 patients had had several years of experience with implant-supported overdentures. During the first year, the mean overall satisfaction among these 17 patients increased from less than 70 to over 90 out of 100 (standardized visual analogue scale). No unusual difficulties were encountered in rendering the treatment or maintaining the attachments. This report offers preliminary evidence of the excellent potential of these magnets for retaining mandibular implant-supported overdentures.

Implant overdenture using Konus telescope on one-piece implant: a case report

An implant-retained Konus (tapered double crown) telescopic complete overdenture was fabricated for a mandibular edentulous patient. The Konus telescopic overdenture coping crowns and framework assembly were cast with commercially pure (CP) titanium, joined using laser welding and placed on four one-piece implants. Sufficient retention and stability were obtained using this method.

A resin acrylic and plaster solder index technique for realigning an ill-fitting fixed partial denture framework

A resin acrylic and plaster solder index technique is a simple, accurate, secure, and cost-effective way to intraorally realign an ill-fitting fixed partial denture framework. Once the fixed partial denture framework is sectioned and segments are found to fit, an intraoral index preserves the correct relationship among segments and holds castings together securely enough to avoid separating until they can be embedded in solder investment and soldered in the dental laboratory. This technique is described here, together with a literature review and a discussion of the technique's advantages relative to other indexing techniques and materials.

Laser welding of removable partial denture frameworks

PURPOSE

To identify and measure distortions inherent in the casting process of a Class III mandibular cobalt-chromium (Co-Cr) framework to illustrate the problems faced by the laboratory technician and the clinician and to measure the changes that occur during the correction of the fit discrepancy using laser welding.

MATERIALS AND METHODS

Five identical castings of a Co-Cr alloy partial denture casting were made and measured between 3 widely separated points using the x, y, and z adjustments of a Nikon Measurescope. The same measurements were made after each of the following clinical and laboratory procedures: sprue removal, sectioning of the casting into 3 parts through the posterior meshwork, fitting the segments to the master cast, picking up the segments using resin, and laser welding of the 3 segments.

RESULTS

Measurements of all 5 castings showed a cross-arch decrease after sprue removal, an increase after fitting the segments to the master cast, and a slight decrease after resin pickup and laser welding.

CONCLUSIONS

Within the limitations of this study, the findings suggest that precise tooth-frame relations can be established by resin pickup and laser welding of segments of Co-Cr removable partial denture frameworks.

A simplified method to assess precision of fit between framework and supporting implants: a preliminary study

PURPOSE

To present a simplified method for assessment of precision of fit between screw-retained frameworks and supporting implants in clinical situations.

MATERIALS AND METHODS

Torque-angle signature analysis is a method for analysis of tension within a joint. The OsseoCare device developed by Nobel Biocare was utilized for the tests. Three titanium frameworks were fabricated on the same master cast according to 3 different methods: (1) 1-piece casting, (2) the CNC (computer numeric controlled) method, and (3) the CTiP (Cresco Ti Precision) method. These frameworks were used to test the device and indirectly the application of the torque-angle signature analysis technology.

RESULTS

The frameworks fabricated according to the CNC and CTiP methods demonstrated OsseoCare tracings similar to the reference models of passively fitting joints, while the 1-piece cast framework did not.

CONCLUSION

According to this pilot study, the OsseoCare device and torque-angle signature analysis proved to be feasible for clinical assessment of fit between frameworks and supporting implants.

Micro-XRD study of beta–titanium wires and infrared soldered joints

OBJECTIVE

The purpose of this study was to investigate the metallurgical phases in beta-titanium soldered joints prepared by infrared soldering, using the Micro X-ray diffraction technique (Micro-XRD), and to characterize the Vickers hardness in the soldered beta-titanium wires.

METHODS

Beta-titanium wires with cross-section dimensions of 0.032in.x0.032in. (TMA, Ormco), and both titanium-based solder (Ti-30Ni-20Cu, Selec) and silver-based solder (Ag-22Cu-17Zn-5Sn, Tomy) were selected. Soldering was performed using infrared radiation (RS-1, Morita) under argon atmosphere. Micro-XRD analyses were performed at room temperature. Micro-XRD spectra were obtained for the boundary region of the soldered beta-titanium wires using 50microm and 10microm diameter analysis regions. Hardness was measured at 30microm intervals from boundary of the diffusion layer and beta-titanium wire. The Kruskal-Wallis test with the Bonferroni and Wilcoxson Mann-Whitney tests for nonparametric means were employed as statistical methods (P<0.05).

RESULTS

For both types of soldered beta-titanium samples, the Micro-XRD spectra contained four major peaks for body-centered cubic (bcc) beta-titanium. Additional peaks at about 41 and 45 degrees are attributed to Cu-Ti intermetallic phase(s), which may be metastable under soldering conditions. The diffusion layer had greater hardness than bulk beta-titanium for both types of soldered specimens (P<0.05).

SIGNIFICANCE

Soldering of beta-titanium orthodontic wire by infrared radiation may be acceptable for clinical use, since Micro-XRD spectra revealed that both types of soldered specimens largely retained the bcc beta-titanium structure. Further research is needed to investigate the mechanical properties and corrosion behavior of infrared-soldered beta-titanium wire.

Sagittal and vertical load-deflection and permanent deformation of transpalatal arches connected with palatal implants: an in-vitro study

INTRODUCTION

The purposes of this laboratory investigation were to (1) measure the sagittal and vertical deflection of loaded transpalatal arches (TPAs) connected to a palatal implant, (2) measure the extent of permanent deformation of the connecting TPA in the sagittal and vertical directions, (3) test various wire dimensions in terms of deflection behavior, and (4) evaluate soldering vs laser welding vs adhesive bonding of TPAs in terms of load deflection behavior.

METHODS

Stainless steel wires of 6 dimensions were tested: 0.8 x 0.8, 0.9, 1, 1.1, 1.2, and 1.2 x 1.2 mm. For each dimension, 10 specimens were soldered to the palatal implant abutment, 10 were laser welded, and 10 were adhesively bonded to the implant abutment (total, 180 specimens). The measuring device applied increments of force of 50 cN, from 0 to 500 cN. Then the specimens were unloaded. The values were statistically described and analyzed with ANOVA and Wilcoxon rank sum tests.

RESULTS AND CONCLUSIONS

Absolute orthodontic anchorage without deformation of TPAs was not observed with the wire dimensions tested. To prevent loss of anchorage greater than 370 mum (sagittal deflection of 1.2 x 1.2 mm adhesively bonded TPA at 500 cN force level), wires thicker than 1.2 x 1.2 mm or cast anchorage elements must be considered for clinical practice. However, larger cross sections might cause more patient discomfort, and laboratory procedures increase costs.

Joining characteristics of orthodontic wires with laser welding

Laser welding 0.016 x 0.022 in. beta-Ti, Ni-Ti, and Co-Cr-Ni orthodontic wires was investigated by measuring joint tensile strength, measuring laser penetration depth, determining metallurgical phases using micro X-ray diffraction (micro-XRD), and examining microstructures with an scanning electron microscope (SEM). Welding was performed from 150 to 230 V. Mean tensile strength for Ni-Ti groups was significantly lower (p < 0.05) than for most other groups of laser-welded specimens. Although mean tensile strength for beta-Ti and Co-Cr-Ni was significantly lower than for control specimens joined by silver soldering, it was sufficient for clinical use. The beta-Ti orthodontic wire showed deeper penetration depth from laser welding than the Ni-Ti and Co-Cr-Ni orthodontic wires. Micro-XRD patterns of laser-welded beta-Ti and Ni-Ti obtained 2 mm from the boundary were similar to as-received specimens, indicating that original microstructures were maintained. When output voltages of 190 V and higher were used, most peaks from joint areas disappeared or were much weaker, perhaps because of a directional solidification effect, evidenced by SEM observation of fine striations in welded beta-Ti. Laser welding beta-Ti and Co-Cr-Ni wires may be acceptable clinically, since joints had sufficient strength and metallurgical phases in the original wires were not greatly altered.

Tensile strength and corrosion resistance of brazed and laser-welded cobalt-chromium alloy joints

STATEMENT OF PROBLEM

The longevity of prosthodontic restorations is often limited due to the mechanical or corrosive failure occurring at the sites where segments of a metal framework are joined together.

PURPOSE

The purpose of this study was to determine which joining method offers the best properties to cobalt-chromium alloy frameworks. Brazed and 2 types of laser-welded joints were compared for their mechanical and corrosion characteristics.

MATERIAL AND METHODS

Sixty-eight cylindrical cobalt-chromium dental alloy specimens, 35 mm long and 2 mm in diameter, were cast. Sixteen specimens were selected for electrochemical measurements in an artificial saliva solution and divided into 4 groups (n=4). In the intact group, the specimens were left as cast. The specimens of the remaining 3 groups were sectioned at the center, perpendicular to the long-axis, and were subsequently rejoined by brazing (brazing group) or laser welding using an X- or I-shaped joint design (X laser and I laser groups, respectively). Another 16 specimens were selected for electrochemical measurements in a more acidic artificial saliva solution. These specimens were also divided into 4 groups (n=4) as described above. Electrochemical impedance spectroscopy and potentiodynamic polarization were used to assess corrosion potentials, breakdown potentials, corrosion current densities, total impedances at lowest frequency, and polarization charge-transfer resistances. The remaining 36 specimens were used for tensile testing. They were divided into 3 groups in which specimen pairs (n=6) were joined by brazing or laser welding to form 70-mm-long cylindrical rods. The tensile strength (MPa) was measured using a universal testing machine. Differences between groups were analyzed using 1-way analysis of variance (alpha=.05). The fracture surfaces and corrosion defects were examined with a scanning electron microscope.

RESULTS

The average tensile strength of brazed joints was 792 MPa and was significantly greater (P<.05) than the tensile strength of both types of laser-welded joints (404 MPa and 405 MPa). When laser welding was used, successful joining was limited to the peripheral aspects of the weld. The welding technique did not significantly affect the joint tensile strength. Electrochemical measurements indicated that the corrosion resistance of the laser-welded joints was better than of the brazed ones, primarily due to differences in passivation ability.

CONCLUSION

Laser welding provides excellent corrosion resistance to cobalt-chromium alloy joints, but strength is limited due to the shallow weld penetration. Brazed joints are less resistant to corrosion but have higher tensile strength than laser welds.

Physical and metallurgical considerations of failures of soldered bars in bar attachment systems for implant overdentures: a review of the literature

The purpose of this literature review was to identify the etiological factors of failure of soldered bars in bar attachment systems for removable implant overdentures. A search of MEDLINE using the key words "bar attachment systems" was performed of English language peer-reviewed journals published between 1975 and 2005. Clinical studies of implant overdentures with prosthodontic maintenance complications of bar attachment systems were identified to establish the perceived etiology of failure. A further search of MEDLINE using the key words "solder joint" was also performed of the fixed prosthodontic literature to identify specific factors affecting the strength, fatigue resistance, and quality of gold solder joints used for bar attachment systems. The first search on bar attachment systems produced evidence of low failure rates of interabutment bars, but higher failure rates of bars where distal cantilever extensions were used. There were no explanations or descriptions of the nature of those failures in the clinical studies reviewed. The second search on fixed prosthodontic literature identified multiple factors that could potentially relate to the failed solder joints with bar attachments. Two potential sites of failure in bar attachments with distal cantilevers were identified, and a simple estimate of the tensile stresses at the solder joints was performed. The values found are comparable to the fatigue failure stresses reported in the searched literature.

[Structural characteristics of laser-welded cast pure titanium joints by different gap distance]

OBJECTIVE

To measure the microstructure of laser-welded cast pure titanium by different gap distance.

METHODS

Forty specimens were sectioned and welded at four gaps (0.00 mm, 0.25 mm, 0.50 mm and 1.00 mm). Took microhardness test and metallographic examination of welded zone surface.

RESULTS

There were no difference in microhardness value and metallographic observation between welded specimens. The width of heat-effected zone was different. The smaller grains and needle-like alphamartensitic structure were found in the heat-affected zone.

CONCLUSION

The effects of the joint gap were not significant.

Clinical Experiences with Laser-Welded Titanium Frameworks Supported by Implants in the Edentulous Mandible: A 10-Year Follow-Up Study

BACKGROUND

Long-term follow-up studies for more than 5 years are not available on laser-welded titanium frameworks.

PURPOSE

To report and compare 10-year data on implant-supported prostheses in the edentulous mandible provided with laser-welded titanium frameworks and conventional gold alloy frameworks.

MATERIALS AND METHODS

Altogether, 155 patients were consecutively treated with prostheses at abutment level with two generations of fixed laser-welded titanium frameworks (test groups). A control group of 53 randomly selected patients with conventional gold alloy castings was used for comparison. Clinical and radiographic 10-year data were collected for the three groups.

RESULTS

All patients followed-up for 10 years (n=112) still had fixed prostheses in the mandible (cumulative success rate [CSR] 100%). The overall 10-year cumulative success rate (CSR) was 92.8 and 100.0% for titanium and gold alloy frameworks, respectively. Ten-year implant cumulative survival rate (CSR) was 99.4 and 99.6% for the test and control groups, respectively. Average 10-year bone loss was 0.56 (SD 0.45) mm for the titanium group and 0.77 (SD 0.36) mm for the control group (p < 0.05). The most common complications for titanium frameworks were resin or veneer fractures, soft tissue inflammation, and fractures (12.9%) of the metal frame. Loose and fractured implant screw components were below 3%.

CONCLUSION

Excellent overall long-term results with 100% CSR could be achieved with the present treatment modality. Fractures of the metal frames and remade prostheses were more common for the laser-welded titanium frameworks, and the first generation of titanium frameworks worked poorly when compared with gold alloy frameworks during 10 years (p < 0.05). However, on average more bone loss was observed for implants supporting gold alloy frameworks during 10 years. The reasons for this difference are not clear.

Bilateral space maintainers: a 7-year retrospective study from private practice

PURPOSE

The purpose of this study was to report survival times and problems encountered with bilateral space maintainers placed over a 7 year period.

METHODS

Charts were reviewed for all patients who had bilateral space maintainers placed between January 1, 1996 and December 31, 2003. Appliance lifetime and problems encountered were recorded and assessed on July 30, 2005, if still in use. Failures were recorded as: (1) cement loss; (2) solder breakage; (3) split band; (4) eruption interference; (5) bent wire; (6) loss; or (7) not specified. Also recorded were: (1) failed appliances; (2) transferred patients; and (3) those lost to follow-up.

RESULTS

A total of 482 space maintainers were evaluated, with 114 failures (24%) and 349 successes (72%). Of the 114 known failures: 68 (60%) were from cement loss; 12 (10%) were from solder breakage; 11 (10%) were from split bands; and 13 (11%) were from reasons not specified. No statistical differences were noted between types of failures or between genders. Mean pooled survival times were 20 months for lingual arches and 23 months for Nance appliances, with no statistical differences between arches, except in successful appliances where Nance was superior (P = .011). Of the 114 failed appliances: 44 (39%) were not recemented or remade, which was considered clinically successful; 51 (45%) were recemented; and 19 (17%) were remade. Eight appliances were lost to follow-up or transferred.

CONCLUSION

The majority of bilateral space maintainers (72%) lasted their anticipated lifetimes.

Microstructures of beta-titanium orthodontic wires joined by infrared brazing

The microstructures and interdiffusion in brazed beta-titanium orthodontic wires were investigated by scanning electron microscopy and electron probe microanalysis, respectively. Beta-titanium wire (Ti-11Mo-6Zr-4Sn) with cross-section dimensions of 0.032 in. x 0.032 in., titanium-based braze alloy (Ti-30Ni-20Cu), and silver-based braze alloy (Ag-22Cu-17Zn-5Sn) were selected for the study. Brazing was performed using infrared radiation (RS-1) under an argon atmosphere. Specimens were etched with two solutions (2.5% HF + 2.5% HNO(3) + 95% H(2)O; 25% HN(4)OH + 30% H(2)O(2) + 45%H(2)O). It was found that the silver-based braze alloy has a eutectic structure. In the diffusion layer between the beta-titanium wire and this silver-based braze alloy, Cu and Ti were enriched on the wire side, and Sn and Ti were enriched on the braze alloy side. The titanium-based braze alloy has a dendritic structure. Beta-titanium wire specimens brazed with the titanium-based braze alloy had a thicker intermediate area compared to the silver alloy; Ti in the diffusion layer had an irregular concentration gradient, and the braze alloy side had higher Ti concentration. The original microstructure of the beta-titanium wire was not altered with the use of either braze alloy. Infrared brazing of beta-titanium orthodontic wire is acceptable for clinical use, since the wire microstructure did not deteriorate with either the titanium-based or silver-based braze alloy. The differing microstructures of the joint regions for the two braze alloys suggest that the joint strengths may also differ.

Failure investigation of soldered stainless steel orthodontic appliances exposed to artificial saliva

Globally in the field of Dental Technology, soldering continues to be the prevailing joining technique for removable orthodontic appliances. The strength of the soldered joint, however, is a growing concern to dental technicians since the commonly employed silver solder undergoes accelerated corrosion and ultimately influences the success of orthodontic appliances intraorally.

OBJECTIVE

The goal of this in vitro study was to determine the effects of exposure to artificial saliva on the mechanical strength of orthodontic silver-soldered stainless steel joints.

METHODS

One hundred (control group n=20; aged group n=80) soldered specimens were exposed to varying exposure times in Fusayama's artificial saliva. Tensile failure loads of the control and aged groups were measured. Failure modes were evaluated by examining the exposed surfaces, solder microstructure and the fracture morphology using a combination of light microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

RESULTS

A marked decrease in tensile failure load of the joints was recorded after exposure to artificial saliva. Selective attack was identified on the aged solder surfaces, which was attributed to the micro-galvanic effect brought about by the preponderance of Cu-rich phases in the solder microstructure. The selective attack promoted decohesion at the solder/wire interface, thereby reducing the tensile failure load.

SIGNIFICANCE

This study helped to elucidate that an association between exposure periods and microstructure of soldered orthodontic joints exists and that their combined effects positively influence the tensile strengths of orthodontic soldered joints.

[Application of the laser welding to preventing the break of the base plate caused by the increase of magnetic attachments]

OBJECTIVE

This study was intended to design a kind of resisting part dint of device in order to preventing the base plate break while being subjected to the dint when partial base plate dint concentrates because of the increase of the magnetic attachment to the original movable artificial teeth.

METHODS

Ten patients who should increase magnetic attachment was adopted in the study, and we increased a kind of new designed partial cast base plate on the original base plate using laser welding technique, then designed magnetic attachment and artificial teeth.

RESULTS

None of ten sufferers appeared the phenomenon of the break of the base plate.

CONCLUSION

The application of the laser welding technique can prevent the break of the base plate when partial dint increase because of the increase of the magnetic attachments.

Bond strength of luting cement to casting and soldering alloy

Adjustment of metal alloy framework of the porcelain-fused-to-metal crown by soldering minor marginal deficiences prior insertion may sometimes be needed. The aim of this study was to compare shear bond strengths of four luting cements to casting metal alloy and soldering metal alloy. A total of 64 flame cast non-precious metal alloy and flame soldered metal alloy samples were used. Durelon, Panavia F, RelyX Unicem Applicap and RelyX ARC stubs were bonded to the alloy substrate surface. After stored in water at 37 degrees C for 1 week, shear bond strength of the cement to the alloy was measured. Differences were analyzed using one way ANOVA (p<0.05). There were no difference between the cast metal alloy and soldering metal alloy substrate.

Noncompliant treatment of skeletal open bite

The purpose of this article is to illustrate the effects of the rapid molar intrusion appliance, a treatment alternative that does not require patient compliance, for counteracting excessive vertical dimensions in growing patients and adults. The rapid molar intrusion appliance has 2 elastic modules that are secured on the maxillary and mandibular first-molar tubes. It is used in combination with maxillary and mandibular soldered lingual arches. Patient acceptance is good, and the patient's only responsibilities are to keep the appliance clean and avoid breakage.

Basic evaluation of cast joining for electroformed coping using multi-purpose alloys

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800 degrees C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750 degrees C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

Effect of soldering on the metal-ceramic bond strength of an Ni-Cr base alloy

STATEMENT OF PROBLEM

Although soldering is a common laboratory procedure, the use of soldering alloys may adversely affect metal-ceramic bond strength and potentially decrease the longevity of metal-ceramic restorations.

PURPOSE

The purpose of this study was to investigate the effect of soldering on metal-ceramic bond strength of a representative Ni-Cr base metal alloy.

MATERIAL AND METHODS

Twenty-eight rectangular (25 x 3 x 0.5 mm) Ni-based alloy (Wiron 99) specimens were equally divided into soldering (S) and reference (R) groups. Soldering group specimens were covered with a 0.1-mm layer of the appropriate solder (Wiron-Lot) and reduced by 0.1 mm on the opposite side. Five specimens of each group were used for the measurement of surface roughness parameter (R(z)) and hardness, and 3 were used for measurement of the modulus of elasticity. Six specimens of each group were covered with porcelain (Ceramco 3) and subjected to a 3-point bending test for evaluation of the metal-ceramic bond strength according to the ISO 9693 specification. The data from surface roughness, hardness, modulus of elasticity, and metal-ceramic bond strength were analyzed statistically, using independent t tests (alpha=.05).

RESULTS

Statistical analysis of the R(z) surface roughness parameter (S: 3.4 +/- 0.3 mum; R: 3.7 +/- 0.7 microm; P=.07) and bond strength (S: 46 +/- 3 MPa; R: 40 +/- 5 MPa; P=.057) failed to reveal any significant difference between the 2 groups. The specimens of the soldering group demonstrated significantly lower values both in hardness (S: 128 +/- 11 VHN; R: 217 +/- 4 VHN; P<.001) and in modulus of elasticity (S: 135 +/- 4 GPa; R: 183 +/- 6 GPa; P=.035) than the reference group.

CONCLUSION

Under the conditions of the present study, the addition of solder to the base metal alloy did not affect the metal-ceramic bond strength.

Joint Properties of Cast Fe-Pt Magnetic Alloy Laser-welded to Co-Cr Alloy

This study investigated the joint properties of Fe-Pt alloy laser-welded to Co-Cr alloy. Cast plates (0.5 x 3.0 x 10 mm) were prepared with Fe-Pt and Co-Cr alloys. Fe-Pt plates were butted against Co-Cr plates and laser-welded using Nd:YAG laser. Control and homogeneously welded specimens were also prepared. Laser welding was performed with and without argon shielding. Tensile testing was conducted, and both fracture force (Ff: N) and elongation (El: %) were recorded. There were no differences in the Ff value between the specimens with and without argon shielding for the welded Fe-Pt/Co-Cr. Lower Ff value of the welded specimen was obtained in the order of Fe-Pt alloy < Fe-Pt/Co-Cr < Co-Cr alloy. The results indicated that Fe-Pt welded to Co-Cr had Ff values between the values of homogeneously welded Fe-Pt and Co-Cr alloys. Argon shielding, on the other hand, had no effect on the weld strength between Fe-Pt and Co-Cr alloys.

Mechanical Strength and Microstructure of Laser-welded Ti-6Al-7Nb Alloy Castings

Mechanical properties of laser-welded castings of Ti-6Al-7Nb alloy, CP Ti, and Co-Cr alloy were investigated and compared to the unwelded castings using a tensile test. Dumbbell-shaped specimens were cut at the center, and two halves of the specimens were welded with an Nd:YAG laser welding machine at 220 or 260 V of laser voltage. The mechanical strength of 260 V groups was higher than that of 220 V groups for Ti-6Al-7Nb and Co-Cr alloys except for CP Ti. All 260 V laser-welded castings of Ti-6Al-7Nb alloy and CP Ti, which fractured outside the welded joints, exhibited ductile characteristics, while all laser-welded Co-Cr alloy castings, which fractured within the welded joints, showed brittle characteristics. This study proved that the mechanical strength of laser-welded Ti-6Al-7Nb alloy and CP Ti castings was as high as that of unwelded castings, while the mechanical properties of laser-welded alloy joints were influenced by microstructural changes.

Lasers in dental implantology

The parallels in the expansion of implant dentistry and laser dentistry in clinical practice are apparent. As advocates for laser dentistry continue to seek new ways to use the technology and as more practitioners become involved in implant dentistry, it is logical to see the concurrent use of both technologies in clinical practice. This article provides data that clearly support the value of dental lasers in the practice of implant dentistry. The challenge for the practitioner is the same as for any other area of dentistry: knowing when, where, and what armamentarium to use in any given situation. Not all dental laser wavelengths are necessarily useful in every dental implant situation. After clinicians know the characteristics of the wavelengths available to them, the application of the technology to the specific situation certainly is warranted.

[Effect of laser irradiation power on the mechanical properties of Co-Cr and Ni-Cr laser-welded joints.]

PURPOSE

To investigate the effect of different irradiation power on the mechanical properties of laser-welded joints.

METHODS

The standard tensile test and three-point bending test rods made from Co-Cr and Ni-Cr alloy were laser-welded with different irradiation powers. Then the tensile rods were tested for the ultimate tensile strength (UTS), and the bending rods for the ultimate bending strength (UBS). The tensile fracture surface was examined by scanning electron microscopy (SEM). Metallurgical analysis and microhardness test were also performed on polished longitudinal sectioned samples.

RESULTS

For Co-Cr alloy, greater irradiation power resulted in greater UTS, minor UBS. For Ni-Cr alloy, there was no significant difference of UTS and UBS between the four groups. SEM and metallurgical examination showed that the welded zone exhibited more gas pores and cracks as the irradiation power increased. Microhardness test showed that hardness increased toward the center of the welded zone and as the irradiation power increased, the range of hardness increased was expanded.

CONCLUSION

The optimal laser irradiation power was the key to achieved superior mechanical properties joints.

Weld characteristics of orthodontic archwire materials

Welding attachments to archwires can produce change in their physical as well as mechanical properties. This study evaluated three archwire alloy materials-stainless steel, Beta titanium, and Timolium for their weld characteristics. The study was divided into tensile-shear test using instron universal testing machine, surface evaluation with the help of scanning electron microscope, and metallographic examination with optical microscope. Six specimens were used for evaluation of each parameter. Increased strength in tensile-shear test and smooth surface and characteristic nugget formation in scanning and optical micrographs, respectively, clearly indicated superior weld characteristics for Beta titanium alloys when compared with the other two archwire alloys. Stainless steel was found to be intermediate in nature, whereas Timolium exhibited poor weld characteristics.

Elemental composition of brazing alloys in metallic orthodontic brackets

The aim of this study was to assess the elemental composition of the brazing alloy of representative orthodontic brackets. The brackets examined were Gemini (3M, Unitec, Monrovia, Calif), MicroLoc (GAC, Bohemia, NY), OptiMESHxrt (Ormco, Glendora, Calif), and Ultratrim (Dentarum, Ispringen, Germany). Four metallic brackets for each brand were embedded in epoxy resin and after metallographic grinding and polishing were cleaned in a water ultrasonic bath. Scanning electron microscopy and energy-dispersive x-ray microanalysis (EDS) were used to assess the quantitative composition of the brazing alloy. Four EDS spectra were collected for each brazing alloy, and the mean value and standard deviation for the concentration of each element were calculated. The elemental composition of the brazing alloys was determined as follows (percent weight): Gemini: Ni = 83.98 +/- 1.02, Si = 6.46 +/- 0.37, Fe = 5.90 +/- 0.93, Cr = 3.52 +/- 0.34; MicroLoc: Ag = 42.82 +/- 0.18, Au = 32.14 +/- 0.65, Cu = 24.53 +/- 0.26, Mg = 1.12 +/- 0.33; OptiMESHxrt: Au = 67.79 +/- 0.97, Fe = 15.69 +/- 0.29, Ni = 13.01 +/- 0.93, Cr = 4.01 +/- 0.35; Ultratrim: Ag = 87.97 +/- 0.33, Cu = 10.51 +/- 0.45, Mg = 1.29 +/- 0.63, Zn = 1.13 +/- 0.24. The findings of this study showed that different brazing materials were used for the different brands, and thus different performances are expected during intraoral exposure; potential effects on the biological properties also are discussed.

The effect of time lapse on the accuracy of two acrylic resins used to assemble an implant framework for soldering

STATEMENT OF PROBLEM

There are insufficient data on the accuracy of resin indexing materials for the assembly of implant prostheses in vivo.

MATERIAL AND METHODS

This in vitro study assessed the fit of an implant framework with the use of 2 common acrylic resins.

PURPOSE

A standardized type IV gold alloy cast framework with 3 stainless steel implant replicas secured to 3 premachined gold cylinders placed 200 mm apart using a parallelometer was fabricated on a flat type IV stone model. Wax was placed around the center of each bar section, and a silicone matrix was fabricated to enable the same quantity of material to be used for each assembly. Each bar was sectioned at the center of the matrix, and indices (n=20) were fabricated from Duralay and GC Pattern acrylic resins. The materials were allowed to polymerize for 15 minutes before the assemblies were removed from the model. Frameworks were visually assessed for fit after an additional 15 minutes, after 2 hours, and after 24 hours, using the Sheffield 1-screw test. Observational outcomes are presented indicating visually perceived fit relative to the type of indexing resin.

RESULTS

Both indexing materials were judged to be visually accurate at the 15-minute time interval only.

CONCLUSION

Within the limitations of this in vitro study, both resin-indexed implant assemblies were judged visually accurate for fit 15 minutes after polymerization but not at subsequent test intervals.

The lingual arm cantilever

The use of cantilevers has been popularized again for use with implant-supported prostheses. A fulcrum, the center of rotation, is usually established on the terminal unit when the cantilever unit moves tissueward (compression) and the anterior units move occlusally (tension). The lingual arm cantilever is another suggested approach that could change the position of the fulcrum forward so that the most distal implant counteracts the rotation. This article describes the procedure to incorporate the lingual arm cantilever into an implant-supported prosthesis.

A simplified method to reduce prosthetic misfit for a screw-retained, implant-supported complete denture using a luting technique and laser welding

An important aim of implant-supported prostheses is to achieve a passive fit of the framework with the abutments to limit the amount of stress transfer to the bone-implant interface. An efficient and standardized technique is proposed. A definitive screw-retained, implant-supported complete denture was fabricated for an immediately loaded provisional screw-retained implant-supported complete denture. Precise fit was achieved by the use of industrial titanium components and the passivity, by an intraoral luting sequence and laser welding.

Titanium removable partial denture clasp repair using laser welding: a clinical report

This clinical report describes repair of a fractured removable partial denture clasp using laser welding rather than a conventional torch soldering technique.

A comparative evaluation of the tensile strength of silver soldered joints of stainless steel and cobalt chromium orthodontic wires with band material--an in vitro study

The present study was conducted to compare and evaluate the tensile strength of silver soldered joints of stainless steel and cobalt-chromium orthodontic wires with band material. An attempt was made to observe the effect of joint site preparation by incorporation of tack welding and increasing metal to metal surface contact area by flattening an end of the wire prior to soldering along with the regularly used round wires without tack welding. A total of 180 wire specimens were soldered to 180 band specimens. Fifteen samples according to joint site preparation were included for each of the wire groups i.e. Gloria (S.S.), Remanium (S.S.) and Remaloy (Co-Cr) wires of 0.036" in diameter. The findings of the study were suggestive that all three wires may be used for preparing silver soldered joints irrespective of the quality of the wire. However, when subjecting the wire to joint site preparation, Gloria (S.S.) wire showed less tensile strength as compared to Remanium and Remaloy.

Distortion of Laser Welded Titanium Plates

The distortion of laser welded titanium plates was assessed for different operating conditions of the laser welding device, and with different welding parameters (in terms of weld point and prewelding). In this study, Nd : YAG laser welding device was used to join the titanium plates. The results showed that distortion increased stepwise after each welding point along the welding zone (one-side welding), but decreased consecutively as the welding proceeded on the second side of the weld (two-side welding). In the case of one-side welding, the dependence of distortion on current and spot diameter presented maxima--due to changes in the welding pool characteristics. For two-side weld the same parameters exercised little influence on its distortion recovery, due to the effect of solidified weld pools from the first side. Current and spot diameter determined the weld pool, which in turn regulated distortion based on shrinkage. Four-point prewelding significantly decreased the final distortion for both one- and two-side welds. Alternating two-side welding of prewelded assembly showed lower distortion than a classic two-side weld.

Effects of local cooling rate and processing variables on leucite in dental porcelain

PURPOSE

This research determined whether there is a measurable effect of local geometry factors on leucite content of dental porcelain in fixed partial dentures (FPD).

MATERIALS AND METHODS

Four-unit FPD frameworks (n = 36) were fabricated using a nickel-chromium alloy (Rexillium III). Body porcelain (Crystar, shade A2) was applied in one increment and subjected to two simulated body firings, followed by a simulated glaze firing to achieve a thickness of 1.5 to 2.0 mm. The completed FPD specimens were randomly assigned to three groups of 12 specimens each: (1) simulated post-soldering, (2) multiple firing, and (3) control. The FPDs from each test group were sectioned into individual units: canine retainer, premolar pontic, molar pontic, and molar retainer. The porcelain was removed from each unit, and the leucite content was measured via quantitative x-ray diffraction.

RESULTS

Porcelain cracking indicated that the soldering simulation had successfully reproduced conditions in the dental laboratory that result in porcelain cracking during soldering. The leucite content was not significantly different between the retainer and pontic units for either the soldering simulation or control FPDs, although the canine retainer units did have a slightly lower leucite content than the pooled values of the other units. Comparison of the pooled data for the three groups indicated statistically significant differences among the leucite contents.

CONCLUSION

Compared to the control, the simulated post-soldering procedure produced a significant increase in leucite, and the multiple firing group exhibited a significant decrease in leucite. Increases in leucite weight fraction during post-soldering operations-and the larger thermally induced stresses that accompany these leucite increases-are responsible for the cracking that occurs.

A modified method of immediate loading using Br�nemark implants in edentulous mandibles

According to the original protocol, Brånemark implants require a two-step surgical procedure in order to become osseointegrated. The two-stage surgery is sometimes uncomfortable for the patient, and recent research has shown that osseointegration can also be achieved with a one-stage technique with early or immediate loading of the implants in good quality bone, which simplifies and shortens treatment for the patient's benefit. The aim of this study was to evaluate the immediate loading of Brånemark implants with a screw-retained prosthesis in edentulous mandibles. Forty-three patients each had three Brånemark implants of varying lengths and diameters installed in the inter-foramina mandibular area. The implant installation procedures were performed according to the standard protocol with avoidance of over-preparation of the implant sites. The prosthesis framework was prefabricated in advance and was cast and separated into three parts, followed by adjustment in the mouth, with a soldering, impression made in situ; finally, the framework was sent to the laboratory for completion of the bridge. The fixed implant bridge was usually delivered to the patient later the same day. Three of the 129 implants failed to osseointegrate, yielding a success rate of 97.6%, with a follow-up period ranging from 3 to 49 months. The results obtained in this study were encouraging, and thus far this modified method of immediate loading in the anterior edentulous mandible appears to be predictable.

Comparison of the load at failure of soldered and nonsoldered porcelain-fused-to-metal crowns

STATEMENT OF PROBLEM

The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns.

PURPOSE

This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens.

MATERIAL AND METHODS

Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm-diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-microm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (alpha=.05).

RESULTS

Mean failure load for nonsoldered crowns was 349 +/- 63 kgf in phase I and 228 +/- 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 +/- 82 kgf [phase I; P<.02] and 154 +/- 108 kgf [phase II; P<.04]) and a greater standard deviation.

CONCLUSION

Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.

The heat-activated solderless passivation (HASP) technique for correcting nonpassive-fitting bars without soldering

The fabrication of a cast noble alloy overdenture bar entails a variety of clinical and laboratory steps, each of which can potentially generate distortions that result in the non-passive fit of the finished product. Traditional laboratory procedures to correct the misfit of cast bars entail sectioning the bar, then reconnecting the bar segments by soldering or welding. After such procedures, research has shown that the bar may still not fit passively on the implant abutments in the patient's mouth. In addition, the overall structure of the bar would be weaker at the mended joints. The heat-activated solderless passivation (HASP) technique involves a two-step process of correcting the master cast, then attaching the cast bar to a soldering index and applying heat to relax the metal until the tensile forces of the retention screws pull the bar into a passive fit.

Implant-supported laser-welded titanium and conventional cast frameworks in the partially edentulous law: a 5-year prospective multicenter study

PURPOSE

This study evaluated and compared the clinical performance of laser-welded titanium fixed partial implant-supported prostheses with that of conventional cast frameworks in the partially edentulous jaw.

MATERIALS AND METHODS

Forty-two patients provided with Brånemark system implants were arranged into two groups. Twenty-one patients (group A) were provided with a conventional cast ceramometal framework in one side of the jaw and a laser-welded titanium framework with low-fusing porcelain in the other side. In group B, 21 patients received a titanium framework prosthesis to replace a conventional implant prosthesis. Clinical and radiographic data were collected for 5 years.

RESULTS

Four implants and one titanium framework were lost during the follow-up period. The two framework designs did not show any significant differences with regard to implant or prosthesis survival (P > .05). Few clinical complications were observed. In group A, marginal bone loss after 5 years was similar for both prosthesis designs, with an average of 0.1 mm and 0.3 mm in the maxilla and mandible, respectively. Basically, no bone loss was observed on average in group B. Furthermore, no significant relationship was observed between marginal bone loss and placement of prosthesis margin or prosthesis design.

CONCLUSION

Except for an insignificant tendency toward a slightly higher incidence of small chips of porcelain veneers, laser-welded titanium frameworks presented an overall similar clinical performance as conventional cast frameworks in partial implant situations after 5 years.