Complete Arch Site Classification for All-On-4 Immediate Function
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Complete arch site classification for all-on-4 immediate function Ole T. Jensen, DDS, MS Greenwood Village, Colo Complete arch immediate function of dental implants requires a treatment protocol that takes advantage of residual areas of cortical bone for the apical fixation of implants. A site and jaw bone classification is proposed that has been in use since 2006 for all stages of atrophy for both jaws. The use of the classification is strictly for immediate function based on specific cortical bone sites in the facial skeleton to assist practitioners in diagnosis, treatment planning, and interdisciplinary communication, as well as to reduce human error in patient management. A recent series of 100 consecutive arches that were treated ac- cording to this classification is presented. (J Prosthet Dent 2014;112:741-751) The first published site classifica- presence or absence of bone. A second The proposed edentulous jaw clas- tion for osseointegrated implants was divergence from previously described sification for immediate function based on vertical bone support for a classifications is the near abandon- implant placement is as follows. 10-mm-long implant.1 The basis of the ment of vertical implant placement, classification was that only 10 mm of which is often problematic in late-stage Class A mandible osseointegration was needed for a atrophy. The reason is that cortical single-tooth implant restoration, a bone can usually be engaged apically The Class A mandible has sufficient theory since validated by several recent with the use of nonaxial implants vertical bone in the posterior to place studies showing that 10 mm or less can placed at a 30-degree angle from the implants above the inferior alveolar be effective.2-8 However, a site classifi- implant entry point.11 By placing im- nerve canal in first molar positions, af- cation for immediate function must be plants in this way, the anterior- ter vertical bone reduction to satisfy entirely different from a site classifica- posterior spread is increased for prosthodontic requirements for inter- tion based on establishing osseointe- improved prosthesis stability. These 2 arch space.15 An anatomic variant of gration via staged implant placement. principles, the presence of cortical the nerve deflecting down toward the The reason is that immediate function bone and an angled implant placement inferior border of the mandible may is concerned primarily with mechanical strategy, strongly suggest a need for exist such that even if the mental fora- fixation, not how much vertical bone is reinterpreting previously published site men area is high, an implant can easily present or how much bone graft classifications of edentulous jaw bone be placed posterior to the foramen. augmentation is needed to optimize morphology. The overarching reason Anterior implants are usually placed osseointgeration.1,9-12 Therefore, site for this is that a classification for im- into canine extraction site locations. classification criteria based on the mediate function must be based on The 4 vertically placed implants are implant length or millimeters of avail- mechanical engineering principles spaced 20 mm or more apart around able bone are not as relevant. For more than on biological (osseointe- the arch (Fig. 1)16 so that the interim- example, a jaw could have abundant gration) principles.13,14 plant arch span exceeds 60 mm. A but low-quality bone incapable of A complete arch site classification cantilevered prosthesis is not necessary establishing primary stability for im- for immediate function implant place- when posterior implants are placed in plants. In contrast, a patient with se- ment with such strict parameters has the first molar locations. vere bone atrophy might still retain not been proposed previously. Howev- small areas of cortical bone able to fix er, it is now important to address the Class B mandible implants for immediate loading. high level of interest in complete arch Therefore, an immediate loading site dental implant reconstruction. The The Class B mandible has several classification is primarily concerned purpose of this article is to propose and millimeters of bone above the inferior with the presence of load bearing bone report on the use of a site classification alveolar nerve canal. This amount of that can mechanically fixanimplant for complete arch immediate function bone allows implant placement slightly and is not merely descriptive of the using 4 implants. posterior to the foramen by angling the Private practice, Greenwood Village, Colo. Jensen 742 Volume 112 Issue 4 are adequate for immediate function in the Class D mandible (Appendix [available online]). Class A maxilla The Class A maxilla, after bone reduction, will have an anatomic variant with a thick palatal wall of bone available 1 Class A: Implants placed in first molar locations as well as medialtothefirst molar extraction site, canine locations for favorable anterior posterior spread. usually just anterior to the palatal root socket. This entry point, angling forward at 30 degrees, will enable implant implant forward to miss the nerve, but midline and extend apically just short of placement into the cortical bone of the not enough for placement of vertical the inferior border in a V formation, palatal wall, avoiding the immediately implants posterior to the foramen. termed the V-4 (Fig. 3).17 The anterior/ adjacent sinus cavity (Fig. 5A,B).25,26 Assuming a 1-mm anterior loopethe posterior (A/P) spread is typically Anterior implants are placed 20 mm or most anterior projection of the inferior reduced to between 10 and 12 mm.17 more forward in the arch but alveolar nerve designated N pointethe The interimplant span of the 4 im- angled back to create an M-shaped implant entry point should be the plants is typically between 30 and 40 patternwhenviewedonapanographic same distance as the bone height above mm. Because the bone is usually highly radiograph.27-29 This implant placement the foramen at N point extending pos- dense, the use of “all-on-3” placement pattern is designated M-4 with all 4 im- teriorly less than 1 to 2 mm to miss the is an option that will slightly increase plants angled at 30 degrees and loop as the implant angles forward at a the A/P spread.22,23 establishes support for a restoration 30-degree angle (Fig. 2A).17-20 (The so- requiring little or no cantilever and with called anterior loop measures 0 to 1 Class D mandible an anterior posterior spread approxi- mm more than 90% of the time.)20 This mating 20 mm and an interimplant arch usually allows for implant placement in The Class D mandible is less than 10 span greater than 60 mm. All implants the second premolar zone for a planned mm in vertical height and corresponds engage the M point, the location of 10-mm cantilever.20 The 2 anterior im- to Cawood Howell Class V-VI atrophy.24 maximum bone mass at the lateral pyri- plants can be placed perpendicular to Three well-spaced implants are used form rim above the nasal fossa.2 When the ridge spaced equidistant. The 4 with the posterior implants angled to- the posterior implant entry point is near implants are spaced up to 15 mm apart ward the midline. The inferior alveolar the first molar apical fixation is often with typical interimplant spans of be- nerve is commonly dehisced and is found in the palatal wall itself as the tween 40 and 45 mm (Fig. 2A). In some usually on top of the ridge, where it can implant body can be placed in parallel patients, buccal to lingual transalveolar easily be reflected with a little manipu- with the palatal wall. The anterior implant placement at a 30-degree angle lation.17 The implant site preparation implant then angles posteriopalatally will be successful posterior to the fora- can then begin in the foramen concavity instead of buccally to fix into this same men in the first molar location. How- itself to improve the A/P spread.17 location within the palatal wall. The net ever, at least 5 mm of vertical bone Screw-tapped implants often perforate effect is that the M point is not engaged should remain above the nerve, and the inferior border.17 A single central as the maximum cortical bone mass but care should be taken not to perforate implant placed vertically completes the 0 is found palatally (designated M point) the lingual wall (Fig. 2B).21 V-3 strategy (Fig. 4). The cantilever in such that implants do not need to tra- the definitive restoration should be verse palatal to buccal to engage the Class C mandible limited to 10 mm, as the A/P spread cortex of the pyriform rim (Fig. 5C). This will likely be between 8 and 12 mm. morphology is only found in robust in- The Class C mandible has little or no The interimplant span varies between dividuals, usually men, but is also a vertical bone above the foramen, and the 25 and 35 mm. The surgeon and general finding of Class A and sometimes angled implant entry point is forward of prosthodontic team should under- Class B sites.7-29 the foramen in the first premolar zone.21 standthatasarchlengthdecreasesin This suggests a 10-mm cantilever the presence of decreased vertical bone without an entire first molar in the height, the risk of implant placement Class B maxilla definitive restoration.22 Anterior im- increases, and a lower number of im- plants are spread at equal distances but plants is required to satisfy load The Class B maxilla has moderate also angled at 30 degrees toward the biomechanics.16 Therefore, 3 implants atrophy and prominent sinus cavities The Journal of Prosthetic Dentistry Jensen October 2014 743 Class C maxilla The Class C maxilla is one in which the alveolar process is absent, the si- nuses project anteriorly and transsinus implant placement is required to obtain an adequate A/P spread.28,29 Some- times implants can be placed at the second premolar area, more often in the first premolar zone.