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24 DENTAL TRIBUNE Middle East & Africa Edition | January-February 2015Implant Tribune By Safa Tahmasebi DDS, MS (USA) Prosthodontist; Costa Ni- colopoulosBDS,FFD(SA) Oral & Maxillofacial Surgeon B ackground With the success of dental implants, the profession of dentistry has moved into apply- ing innovative ideas that have decreased treatment time and amplified the quality of patient’s lives. While integrating into modern dentistry, implant treat- ment has shifted direction from being surgically driven to pros- thetically driven. Amongst other developments in improving all aspect of implant dentistry, an- gled Implants were first intro- duced in the early 1990’s and since then there has been ample research and clinical studies to assess and support their success. (Figure 1) Implants were originally tilted in a bodily fashion to bypass cer- tain anatomical structures that otherwise hindered clinicians from placing them in areas such as the maxillary sinus, inferior alveolar nerve canal, the men- tal foramen, mandibular lingual concavities and maxillary buc- cal concavities. Procedures such as nerve repositioning, various grafting procedures, distraction osteogenesis, ridge splitting and many more not only length- ened treatment time, but also increased patient morbidity dur- ing implant rehabilitation cases. In addition to bypassing the ana- tomical constraints, the tilting of posterior implants in a distal manner results in an increase in the length of the prosthetic table thereby allowing better load dis- tribution, and reducing the can- tilever lengths. Soon with time, tilted implants became an effec- tive and safe alternative to major augmentation procedures such as maxillary sinus grafting pro- cedures and ridge augmentation procedures. Initially there were negative speculations regarding the hard and soft tissue response around tilted implants as opposed to axially straight implants. How- ever various in vitro and in vivo studies have proven no apparent long-term differences between angled and straight implants. Krekmanov et al in 2000 fol- lowed up forty-seven consecu- tive patients with tilted implants for forty months and showed no significant difference between tilted and non-tilted implants. A comparative 3D finite element stress analysis conducted by Cases et al in 2008 showed no indication that angled implants create stress-induced problems compared to straight implants. A meta-analysis preformed by Menini et al in 2012 evaluated the outcomes of upright and tilted implants supporting full- arch fixed dentures for the im- mediate rehabilitation of eden- tulous maxillae, after at least 1 year of function. No significant mean difference between tilted and upright implants was found with regards to bone loss. Ros- en et al in 2013 retrospectively evaluated the surgical effect of tilted implants in the severely resorbed edentulous maxilla as opposed to bone grafting and conventional prosthodontics to restore the posterior maxilla. In a ten-year study patients with tilted implants presented a suc- cessful alternative to the more demanding grafting techniques. Angled abutments Furthermore while angled im- plants improved load distribu- tion, reduced augmentation procedures, lessened cost, treat- ment time and eliminated can- tilevers in many cases they did necessitate the use of angled abutments to achieve a paral- lel path for the draw of the final prosthesis. Custom or prefab- ricated abutments were neces- sary to redirect the screw access holes in a common path of inser- tion to aid in the fabrication and installation of the final prosthe- sis. In addition these abutments were also used to redirect the screw access hole in the lingual direction to aid with esthetics of the final restoration. In cases of severe angulations the prac- titioner is limited to the use of cemented restorations with the use of custom made abutments. (Figure 2) Although these abutments are widely used today, they do pre- sent certain disadvantages that warrant mention. Firstly ,the connecting surfaces of custom- made abutments may have casting imperfections that can attract bacteria and bio film ac- cumulation. Secondly ,if used in cemented restorations, they pro- mote the use of cements that can cause untreatable peri-implanti- tis and peri implant mucositis. Thirdly ,thinning of the custom abutment decreases the abut- ment strength that may lead to fractures of the final restoration under severe load. Fourthly,the use of abutments takes up in- terocclusal vertical prosthetic space often needed for the res- toration. Finally in certain cases one may not be able to redirect the screw access whole ligually and mesially to fabricate a screw retained restoration even with the use of prefabricated 17° and 30° angulated abutments. Co-Axis Implant Fortunately the above disadvan- tages can be eliminated by the use of Co-Axis Implants (South- ern Implants ,Irvine,California) introduced eleven years ago af- ter extensive research and test- ing. Co-Axis Implants feature 12°, 24° or 36 ° correction angles (built into the implants) which allowfor implantplacementinto existing native bone without the need of costly, time consuming and painful bone grafting aug- mentation procedures or the use of angulated abutments. When using Co-Axis Implants the fix- ture platform emerges in an optimal esthetic angle and rela- tively parallel to other implants in the arch thereby allowing the fabrication of screw retained full arch restorations. Subsequently the use of cements and costly angled abutments is eliminat- ed. Regarding the strength of Co-Axis Implants, Howes et al showed higher stress analysis on straight implants as opposed to Co-Axis implants and found loads on Co-Axis Implants to be less than that needed to deform fixtures and cause prosthetic complications. (Figure 3) Anterior Maxilla Implants in the esthetic area has been a popular topic in the recent years due to the cata- strophic failures associated with implants in the esthetic region. The difficulty that arises with implants in the esthetic area is related to anatomic limitations and the higher resorptive prop- erty of the buccal plate. The anatomic limitation is the com- mon buccal concavity associated with the pre maxillary region. The anatomic limitations of the anterior maxilla often require either an angulated implant or adjunctive grafting procedures. The use of Co-Axis implants al- lows the operator to place an implant in the extraction socket of an anterior maxillary tooth without pressure on the buccal plate and simultaneously avoid- ing buccal plate perforations. The placement of an implant close to the buccal plate will lead to implant thread exposure after initial healing, not to men- tion the inevitable use of custom made abutments and cemented restoration to correct the severe facial angulations. Consequently by avoiding the use of angled or customized abutments ,the in- flammatory response due the micro gap / cement that may ul- timately lead to crestal bone loss over time is eliminated .Lastly, facial inclination of an implant makes the facial surface of the connecting abutment thinner than usual and hence may lead to fractures and prosthetic com- plications. The Co-Axis angle correction allows for implant placement in the available bone and hence the screw axis hole emerges from the palatal direc- tion allowing the implants to be centralized within the alveolar bony .This angular correction allows for the placement of the implant within the bony housing and hence allowing for a mini- mum of 2mm of buccal bone that will ensure the stability and firmness of the gingival position in the esthetic area. (Figure 4) Posterior area As mentioned earlier the use of angled implants not only aids with the bypassing of anatomic constraints that would otherwise require grafting procedures, but also aids with load distri- bution and the elimination of long cantilevers(Figure 5) .The mental foramen, maxillary sinus and severe concavities can be avoided with the use of angled implants. However this neces- sitates the use of angled abut- ments to correct the severe distal inclination of the implants. The use of the Co-Axis Implants facilitates the avoidance of anatomic limita- tions, shortening of cantilevers, and enables the use of screw retained restoration without the need of angled abutments. The use of angulated abutments is hence not necessary since Co- Axis Implants correct the an- gulation within the body of the Implant. Deciding on the Angle This tapered body implant is available in 12°, 24° and 36° de- gree built in angle , ranging in 4, 5, 6 mm diameter and 8.5mm to 18mm in length. It is currently available in the external hex, Tri-nex and internal octagon connections. In extreme cases for even higher angle correc- tion, the Co-Axis implant can be combined with a 17° or even the 30° angled abutment. With vari- ous angulations available one can make a decision of the an- gle needed by the use of angled direction indicators that may be used to orientate and assess the 3-D position of the desired access hole within the surgical guide(figure 6). The angled di- rection indicator is inserted into the osteotomy and the prosthetic axis is checked regarding the access hole position for screw retention as well as for parallel- ism with other implant fixtures. When the orientation is con- Modern implants from a different angle Figure 1. Tilting of Implants in the early 1990’s Figure 4 a: Co-Axis Implant Placement in the anterior maxilla b: X-ray of a 12 degree Co-Axis Implant Figure 2. Angled abutments Figure 3. Co-Axis Implants in three different connection Figure 5. All-on-4 Restoration using Co-Axis Implants > Page 25