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  1. 1. A D A J ✷ ✷  N CON IO T T A N I U C IN U G ED ARTICLE 3 AFFORDABLE IMPLANT PROSTHETICS USING A SCREWLESS IMPLANT SYSTEM NORMAN J. SHEPHERD, D.M.D. A B S T R A C T It is ironic that use of one of dentistry’s most important develop- Many dentists have been reluc- ments of the last 15 years, predictable implant dentistry, is actually being discouraged by many dentists.1,2 Patients who want implants tant to place dental implants be- often have to search for dentists to provide this care. cause they have found that most Predictable osseointegrated implants have been used in the implants are costly and time-con- United States since 1982, when the Nobelpharma implant (Brånemark system, Nobel Biocare, Gothenburg, Sweden) was in- suming to place and have long- troduced into North America. Unfortunately, many of the tech- term maintenance problems. niques associated with that implant made it difficult and costly to Most of these problems are treat partially edentulous patients. The excessive chair time, com- ponent costs and laboratory expense have limited the use of im- caused by using screws to con- plants to only a few dentists and relatively affluent patients. nect the abutment to the im- Although it has been reported that as many as 40, 50 or even 60 plant, the crown to the abutment percent of general dentists are restoring implants, most of them have used implants in very few cases.3 It has been estimated that or both. The use of a screwless only 4,000 of the 110,000 general dentists in the United States re- implant system and conventional store four or more implant cases a year.4 prosthetics, the author con- In an attempt to promote affordable implant dentistry, and thereby encourage more restorative dentists to treat more of their tends, can make implant den- average patients with implants, I reviewed the literature on the tistry affordable, versatile and techniques being used, which perhaps were based more on histori- easy to incorporate into all gen- cal use than dental common sense. With the use of a screwless im- plant system and elimination or modification of some of the old eral dental practices. techniques, implant prosthetics can be just as affordable as conven- tional crown-and-bridge dentistry. OPERATIVE SETTING The first thing to examine is the reported need for sterility at the level found in hospital operating rooms, or ORs. Professor Per- Ingmar Brånemark, who introduced osseointegration techniques into North America, had a background as an orthopedist, and as such was used to operating under very sterile conditions in hospital ORs.5 It made sense to his team of surgeons and engineers to design an im- plant fixture consistent with their orthopedic experience, and to de- sign a procedure for placing it that required an OR environment. However, this requirement created problems when dentists in 1732 JADA, Vol. 129, December 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.
  2. 2. CLINICAL PRACTICE which allowed easy access to the individual fixtures for ex- amination during the experi- mentation years. It also allowed easy access to the stacked com- ponents for maintenance pur- poses. Unfortunately, screw-re- tained prosthetics created a multiplicity of problems, such as screw loosening and break- age.7-13 Screws are time-consum- ing to place, costly and unpre- dictable. Connecting a crown to an implant has to be one of the most basic acts of implant den- tistry; yet, after 15 years, we still see journal articles about how to keep screws tight. This fact alone raises questions Figure 1. Cross-section of the Bicon implant (Bicon Implant System) demonstrating locking taper. Compare with conventional implant about the entire process. If components. screws are used, the dentist needs not only a variety of screwdrivers, but also expensive torque drivers. An increasing number of clin- icians have begun to realize that use of cement-retained prosthetics is a better tech- nique. One large commercial laboratory in the United States sent letters to all of its dentist customers explaining that it would no longer fabricate im- plants that used screw-retained prosthetics (James R. Glidewell, written communication, Oct. 5, 1993). There are many advan- tages to cement-retained crowns, such as the ability to maintain normal anatomy, im- Figure 2. Bicon abutment ready for final impression. Note the soft-tissue proved esthetics and compensa- maturation and the preformed gingival sulcus. tion for casting inaccuracies. On the other hand, there are many the United States attempted to ticle demonstrating that im- factors that cause implant duplicate their suggestions. plants could be placed successful- screws to loosen: Most health insurance pro- ly in a dental office or a clinic.6 dpoor occlusion; grams would not cover hospital- This eliminates the need for the dparafunctional habits; ization for dental implants, and more costly hospital OR setting. dcantilevers; converting a typical dental op- dpoor component tolerances; PROBLEMS WITH SCREW- eratory into an OR is extremely RETAINED PROSTHETICS dinaccurate castings; time-consuming and expensive. dinadequate tightening; In 1993, a group from New The Brånemark group used dtoo much tightening; York University published an ar- screw-retained prosthetics, dsingle tooth torque. JADA, Vol. 129, December 1998 1733 Copyright ©1998-2001 American Dental Association. All rights reserved.
  3. 3. CLINICAL PRACTICE The literature indicates that the main advantage of screw-re- tained prosthetics is retrievabili- ty, but bridgework retained by temporary cement is much more easily retrievable than a pros- thesis retained by multiple screws. Since neither caries nor sensitive dentin is a problem if cement washes out, there is no real reason not to use temporary cement. Use of cementable pros- thetics for treating natural teeth is the standard in dental schools, and dentists are familiar and comfortable with this approach. Screw-retained prosthetics re- quire totally different techniques and instrumentation that must Figure 3. Crown cemented on Bicon abutment with either temporary or be learned if a dentist wishes to permanent cement. practice implant dentistry. PROBLEMS WITH EXTERNAL HEX This looseness is a predictor of creep continues under occlusal IMPLANTS broken screws. forces; therefore, the preload that The distance across the flats originally had been used when Another concern is the external of the external hex is 2.68 mil- tightening was first accomplished hex-top implant, a configuration limeters, and the diameter of loses its effect and contributes to that has been copied by more the internal thread that passes broken screw problems.18 than a dozen implant compa- through the top is 2.02 mm. The COST-EFFECTIVE nies and has become the indus- distance across the flats should TECHNIQUES FOR try standard for prosthetic at- be greater than 3.03 mm to pre- IMPLANT DENTISTRY tachments. Unfortunately, this vent the hex wall from dilating. design has two inherent prob- Unfortunately, this dilation, Eliminating these expensive prob- lems: metal dilation and embed- which is caused by the wedging lems is one part of creating cost- ment relaxation. action of the screw as it is tight- effective implant dentistry. The Metal dilation. The hex top ened, remains throughout the other part is to use less expensive was designed as a rotational life of the implant.17 techniques for fabricating pros- torque transfer mechanism to Embedment relaxation. A thetics. The first prerequisite, turn the implant into the bone, second problem is embedment then, is to use a true nonrotation- and it successfully performs that relaxation. When two machined al system. Most of these have task.14 Unfortunately, the classi- components are screwed togeth- some sort of a bevel at the abut- cal external hex is a poor way to er with a torque wrench, it will ment-implant interface to provide connect other components. It is tighten to that particular good metal-to-metal contact. not a true antirotational device, torque. After a few minutes, the Friction between the two surfaces and this leads to micromotion, clinician will find that he or she prevents the rotation. Some sys- bacterial leakage and bone cra- can turn the wrench again tems use screws to hold the com- tering.15,16 The 0.7-millimeter slightly to reach that same ponents together. One system, the height of the hex gives very little torque. What is happening is Bicon Implant (Bicon Implant protection against lateral forces, that the slight machining irreg- System), uses a locking taper that and the thinness of the hex walls ularities of the surfaces actually requires no screw at the abut- makes them subject to metal di- flatten and allow the two com- ment-implant interface (Figure 1). lation, which in turn creates ponents to be more closely ap- This is a true nonrotational con- looseness at the top threads. proximated. This flattening or nection that has been used in or- 1734 JADA, Vol. 129, December 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.
  4. 4. CLINICAL PRACTICE TABLE COMPARISON OF LABORATORY COSTS. BICON IMPLANT SYSTEM OTHER IMPLANT SYSTEMS Implant Type Cost Implant Type Cost Bicon Bar* $190 Cast Overdenture Bar O-rings: implants $80 ($40 if done Two implants $450-$1,000 chairside) O-rings: implants $160 ($80 if done Four implants $900-$1,400 chairside) Single Crown Single Crown on Hex Top Porcelain fused to metal $80-$130 (lab fees Cera One-type abutment $500-$700 same as those for (Nobel Biocare Inc.) natural teeth) UCLA $300-$400 * Bicon Implant System. thopedic hip replacements for used for large bridges; perma- those that were used in the many years. It also is used to nent cement generally is used 1960s and 1970s. These systems hold the chuck to the shaft of for single-tooth implants. The used one-piece implants, such the dental lathe. This locking laboratory bills will be the same as blades, screws and subperio- taper allows no micromotion as those for natural tooth pros- steal implants, in which the and also provides a bacterial abutment was part of the im- seal.16 plant and therefore treated When a true nonrotational The ability to use similarly to a natural tooth. abutment such as this is used, conventional pros- Unfortunately, osseointegration the final abutment can be was not as predictable as it was thetic techniques to placed during second-stage with the two-stage implant sys- surgery, and it then is treated restore the implant tems or the more recent one- like a natural tooth. There is no abutment is critical stage unloaded systems. need for healing caps, impres- Modern implant manufactur- for truly cost-effec- sion posts or transfer copings. ers are aware of the problem This eliminates a great deal of tive implant dentistry. and have tried to find an an- inventory and extra office visits. swer. The ITI implant If the abutment needs modifica- thetics, and the chair time is ac- (Strauman) and the Astratech tion, it can be done either out of tually less than that for the fab- implant systems (Astratech) use the mouth before placement or rication of a crown for a natural a beveled abutment-implant in- in the mouth after placement. A tooth. The ability to use conven- terface to address the antirota- number 1557 carbide bur (S.S. tional prosthetic techniques to tional problem. The Calcitek White Burs Inc.) cuts the titani- restore the implant abutment is (Sulzer Calcitek) spline has a um very effectively with mini- critical for truly cost-effective mechanical interlock, and mum heat.19 A temporary crown implant dentistry. The restora- Screw-Vent (Paragon) has an can be placed at the second- tive dentist does not need to internal hex with a slight taper stage visit if needed (areas that purchase an implant prosthetic lock. All of these implant sys- are not esthetically important kit. All of the necessary restora- tems, however, still require a require no temporary crown). tive procedures are familiar to screw to mechanically clamp The final impression is taken the dentist, the office staff and the parts together. after soft-tissue maturation has the dental laboratory. In the case of an edentulous occurred, and the crown is then Ironically, the only other patient, the nonrotational nature cemented in place (Figures 2 screwless implant systems that of these abutments eliminates and 3). Temporary cement is can be used in this manner are the need for a cast bar, and this JADA, Vol. 129, December 1998 1735 Copyright ©1998-2001 American Dental Association. All rights reserved.
  5. 5. CLINICAL PRACTICE in turn allows individual balls or O-ring abutments to be used. If a A patient can afford the surgery necessary to place two implants, then the prosthetic cost of an O- ring–retained overdenture is minimal. These are simpler tech- niques with significantly lower laboratory cost (Table). Much of the fabrication can be done at chairside if the patient already has a well-made denture.20 The locking taper shaft of the Bicon Implant allows for the use of 15- degree O-ring abutments, which is a considerable help in treating maxillary cases. If a patient al- ready has denture support of two balls or O-rings, the dentist can later add additional implants and convert the overdenture to B fixed bridgework, even if the pa- tient has to wear a laboratory- cured provisional bridge for a year or two before he or she can afford the final metal-porcelain bridge. In other words, definitive treatment does not have to be done at one time. A patient can start with a relatively inexpen- sive treatment and then, as he or she can afford it, graduate to a more ideal fixed prosthesis. A true overdenture should be soft-tissue–borne and retained only by the mechanical device attached to the implant. For this reason, it is not necessary Figure 4. A. Four individual premolar and molar crowns—three on Bicon to link the implants. Such link- abutments and the anterior crown on a natural tooth. B. Radiographic age certainly is not needed to appearance. prevent rotation of the individu- al abutments. The flexibility of rotational torque—becomes a ry of normal hygiene tech- these abutments allows a regu- very simple post-and-core pros- niques. Unlike a natural-tooth lar menu of treatment options thetic restoration with screw- crown, the margin of an implant that permit implant dentistry to less implants. Single-molar crown needs to be placed sub- become affordable to the majori- implants can be restored and gingivally only in esthetically ty of dental patients, instead of several single crowns can even important areas. The casting just the wealthy. be placed side by side (Figure can be at or above the gingival The single-tooth implant 4). This obviates the problem level in the mesial, distal or restoration—which in many of inaccurate casting for multi- palatal/lingual areas (Figure 5). systems is extremely difficult, ple crowns. It more closely The single-tooth implant if not impossible, to place in duplicates normal anatomy restoration allows the cost of a posterior areas because of the and allows the patient the luxu- single implant and crown to be 1736 JADA, Vol. 129, December 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.
  6. 6. CLINICAL PRACTICE competitive with that of a three- unit bridge. If a dental practice has a prosthetic unit charge of $600, a three-unit bridge would cost $1,800. The single implant can be placed for $900 to $1,100, and the crown would cost $600, the same as that for a crown on a natural tooth; therefore, the implant and crown would cost $1,500 to $1,700. This allows implant dentistry to be afford- able to most dental patients. Because of the flexibility of angled abutments, full-arch fixed bridges also can be created with abutments prepared for ce- mented prostheses. These an- gled abutments can be rotated a Figure 5. Schematic showing that the crown casting is subgingival only full 360 degrees, and it is there- in the esthetic facial area. It may be at or above the gingival margin in fore relatively easy to mix the mesial, distal or palatal/lingual areas. straight and angled abutments to achieve parallelism. cally direct the surgeon’s bur, ever, to perform implant pros- A very important require- and the implant will be in the thetics in a cost-effective man- ment of cost-effective implant precise location that the ner, which in turn greatly in- dentistry is that the implant is restorative dentist requires. creases the availability of the placed in the proper position. To Such a stent is shown in treatment modality to the gen- do this, an accurate, user- eral dental population. By com- friendly stent or stents should bining a screwless implant The stents I recom- be used. I recommend that a system with simple and famil- palatal or lingual stent be used mended are made iar prosthetic techniques, all to position the implant, and a from waxed-up artic- restorative dentists can provide vacu-press clear stent be used care for their patients who may ulated study models, to ascertain the position of the benefit from implant dentistry. abutment. In most stents that because they me- The four main prerequisites for are discussed in the literature, chanically direct the cost-effective implant dentistry either there is an occlusal posi- are as follows: surgeon’s bur, and tional hole or the buccal cusps dplace the implants in the have been retained. This type of the implant will be in proper position; stent looks very good on a labo- the precise location duse nonrotational abutments; ratory bench, but once in the dprovide for the patient’s fi- that the restorative mouth it often obstructs the nancial and functional needs; surgeon’s vision and prevents dentist requires. duse conventional dental him or her from seeing the tip prosthetics. s of the guide bur and the bone at Figure 6, along with the out- Dr. Shepherd is in private practice with the same time. When a surgeon come of the treatment. Northern Essex Oral Surgery Associates Inc., is uncomfortable with the 390 Water St., Haverhill, Mass. 01830. SUMMARY Address reprint requests to Dr. Shepherd. amount of visibility, he or she often will not use the stent that For the most part, implant den- Dr. Shepherd holds an equity interest in Bicon Implant System. has been made. The stents I tistry today is more expensive recommend are made from and time-consuming than con- 1. Christensen G. Bicon Dental Implants. Clin Res Assoc Newsletter 1996;20(12):2. waxed-up articulated study ventional crown-and-bridge 2. Park N. Implants now simpler. Nobel models, because they mechani- prosthetics. It is possible, how- Biocare Update 1997;8(3):2. JADA, Vol. 129, December 1998 1737 Copyright ©1998-2001 American Dental Association. All rights reserved.
  7. 7. CLINICAL PRACTICE sterile versus clean conditions. J Periodontol 1993;64:954-6. A 7. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: The Toronto Study. Part III: prob- lems and complications encountered. J Prosthet Dent 1990;64:185-94. 8. Jemt T. Failures and complications in 391 consecutively inserted fixed prostheses supported by Brånemark implants in edentu- lous jaws: a study of treatment from the time of prosthesis placement to the first annual checkup. Int J Oral Maxillofac Implants 1991;6:270-6. 9. Tolman DE, Laney WR. Tissue-integrat- ed prosthesis complications. Int J Oral Maxillofac Implants 1992;7:477-84. 10. Naert I, Quirynen M, Theuniers G, van Steenberghe D. Prosthetic aspects of osseoin- tegrated fixtures supporting over-dentures: a 4-year report. J Prosthet Dent 1991;65:671- 80. 11. Jemt T, Linden B, Lekholm U. Failures and complications in 127 consecutively placed fixed partial prostheses supported by Brånemark implants: from prosthetic treat- ment to first annual checkup. Int J Oral Maxillofac Implants 1992;7:40-4. 12. Naert I, Quirynen M, van Steenberghe D. A six-year prosthodontic study of 509 con- B secutively inserted implants for the treatment of partial edentulism. J Prosthet Dent 1992;67:236-45. 13. Kallus T, Bessing C. Loose gold screws frequently occur in full-arch fixed prostheses supported by osseointegrated implants after 5 years. Int J Oral Maxillofac Implants 1994;9:169-78. 14. Beaty K. The role of screws in implant systems. Int J Oral Maxillofac Implants 1994; 9(special supplement):52-4. 15. Balfour A, O’Brien GR. Comparative study of anti-rotational single tooth abut- ments. J Prosthet Dent 1995;73(1):36-43. 16. Muftu A, Mulcahy HL, Chapman R. Comparison of Streptococcus sanguis penetra- tion through various implant connection mechanisms (abstract 585). J Dent Res 1997;76(special issue):87. 17. Blake A. What every engineer should know about threaded fasteners. New York: Marcel Dekker; 1986:32-5. 18. Dixon DL, Breeding LC, Sadler JP, McKay ML. Comparison of screw loosening, rotation, and deflection among three implant designs. J Prosthet Dent 1995;74:270-8. 19. Gros M, Laufer BZ, Oriniamar Z. An in- Figure 6. A. Panoramic radiograph of the mouth in the finished case. B. vestigation on heat transfer to the implant- Clinical view of the mouth in the finished case. bone interface due to abutment preparation with high-speed cutting instruments. Int J 3. Watson MT. Implant dentistry: a ten- International Inc.; 1993:1-27. Oral Maxillofac Implants 1995;10:207-12. year retrospective. Dental Products Report 5. Johansson F. Brånemark System: surgi- 20. Shepherd N. A general dentist’s guide to 1996;30(12):26-31. cal operatory set-up procedures. Westmont, proper dental implant placement from an oral 4. Dental implants: emerging technology Ill.: Nobelpharma USA Inc.; 1994. surgeon’s perspective. Compend Contin Educ trends and oral and maxillofacial and perio- 6. Scharf DR, Tarnow DP. Success rates of Dent 1996;17(2):118-30. dontal surgery. Irvine, Calif.: Medical Data osseointegration for implants placed under 1738 JADA, Vol. 129, December 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.