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FALL 2012 ISSUE
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Implant Position in the Esthetic Zone

animation continuing education

Siamak Abai, DDS, MMedSc

Overview

Proper implant positioning is patient- and often implant-specific, making prosthetic treatment planning and pre-placement protocol paramount for achieving predictable restorative results. Dr. Siamak Abai, staff dentist of clinical research at Glidewell Laboratories, details some of the established parameters with regard to implant spacing and angulation, and highlights the use of advanced tools such as Inclusive® Digital Treatment Planning services and the Inclusive® Tooth Replacement Solution to execute precise control over each individual case. After reviewing the article and accompanying animation, take the CE test to earn two free credits.

About Dr. Abai

wiederholdDr. Siamak Abai earned his DDS degree from Columbia University in 2004, followed by two years of residency in general dentistry. After two years of general private practice in Huntington Beach, Calif., Dr. Abai returned to academia and received an MMedSc degree and a certificate in prosthodontics from Harvard University. Before joining Glidewell in January 2012, he practiced at the Wöhrle Dental Implant Clinic in Newport Beach. Dr. Abai brings nearly 10 years of clinical, research and lecturing experience to his role as staff dentist of clinical research at Glidewell Laboratories. Contact him at inclusivemagazine@glidewelldental.com.

Since the advent of modern root form osseointegrated implant dentistry in 1952 by Per-Ingvar Brånemark1 and colleagues, clinicians have strived for improvements in implant positioning in the esthetic zone to achieve predictable restorative and esthetic results. Years of clinical experience in congruence with controlled clinical studies have led to established parameters as a guide for these results. Prosthetic treatment planning and establishing a set clinical protocol prior to implant placement are paramount. It is important to note that proper implant positioning is patient and often implant-specific, and that inter-patient generalizations can result in myopic treatment planning and decrease the predictability of an esthetic outcome.

Treatment planning prior to implant placement traditionally begins with comprehensive medical and dental evaluation, articulated diagnostic casts, periapical and panoramic radiographs, cone beam computed tomography (CBCT) scans, and a diagnostic wax-up. Patient demands must always be taken into consideration prior to surgery, and presurgical mockups may be necessary to convey the information to the patient. Prosthetic treatment planning helps the clinician with a restorative-driven implant placement rather than a bone-driven approach, with the latter leading to poor abutment angulations and drastically reduced restorative options. Bone augmentation is often necessary in order to achieve optimal residual ridge dimensions prior to implant placement.

The inventive work of Sir Godfrey Hounsfield2 and the advancement of CBCT technology have led the dental profession into a new realm of dimensional accuracy that is often unattainable with conventional dental radiography. In combination with the use of a surgical or guided stent, proper 3-D positioning of a dental implant has become an attainable goal, leading to increased confidence for the clinician and accurate clinical results. The importance of the implant position can be manifested in the four dimensionally sensitive positioning criteria: mesiodistal, labiolingual, and apico-coronal location, as well as implant angulation.3 The ultimate goal is not only to avoid adjacent sensitive structures, but to respect the biological principles that have been established to achieve esthetic results.

MESIODISTAL CRITERIA

Correct implant position in a mesiodistal orientation allows the clinician to avoid iatrogenic damage to adjacent critical structures. Maintaining adequate distance from adjacent teeth also helps preserve crestal bone and interproximal papillary height. When placing an implant adjacent to a tooth, it has been shown that crestal bone peak is based on and maintained by the bone level of the teeth adjacent to the missing space. A minimum distance of 1.5 mm between implant and existing dentition has been determined to prevent damage to the adjacent teeth and to provide proper osseointegration and gingival contours4-6 (Fig. 1a). Implants placed too closely together can reduce the height of the inter-implant bone crest, and a distance of less than 3 mm between two adjacent implants leads to increased bone loss. It has been shown that a distance of more than 3 mm between two adjacent implants preserves the interproximal bone peak and results in 0.45 mm of resorption on average, giving a better chance of proper interproximal papillary height (Fig. 1b). If the space between implants is 3 mm or less, the average resorption of the interproximal bone peak increases to 1.04 mm, compromising support for the interdental papilla.4,7 As a result, wide-bodied implants less than 3 mm apart in the esthetic zone would compromise the desired outcome.

LABIOLINGUAL CRITERIA

Labiolingual implant position is often determined by the gingival biotype, occlusal considerations of opposing teeth, and desired emergence profile. An implant placed too far labially can cause bone dehiscence and gingival recession leading to exposure or show-through of the implant collar. An implant placed too far lingually can cause prosthetic difficulties with ridge-lap restorations that can be unhygienic and unesthetic. A thickness of 1.8 mm of labial bone has been determined to be critical in maintaining an implant soft tissue profile and increasing the likelihood of an esthetic outcome8 (Fig. 2). Labially oriented implants compromise the subgingival emergence profile development, creating long crowns and misalignment of the collar with respect to the adjacent teeth.9

APICO-CORONAL CRITERIA

Peri-implant crestal bone stability plays a critical role in the presence of interdental papilla.10 Many factors contribute to crestal bone resorption, including existing anatomy, surgical trauma, overloading, peri-implantitis, implant surface characteristics, microgap at the implant-abutment junction, type of connection between implant, and prosthetic components.11 Several factors are cause for concern in the apico-coronal placement of implants. Implants placed too shallow may reveal the metal collar of the implant through the gingiva. Countersinking implants below the level of the crestal bone may give prosthetic advantages with more running room for prosthetic components and tissue contouring, but can lead to crestal bone loss due to the location of a microgap at the implant-abutment interface. The ideal solution to exposure of the implant collar would be the placement of an implant equicrestal or subcrestal to the ridge. However, the existing microgap at the implant-abutment junction leads to bone resorption due to peri-implant inflammation.12 It is suggested that an implant collar be located 2 mm apical to the CEJ of an adjacent tooth if no gingival recession is present13 (Fig. 3). Implant diameter also plays a role in apico-coronal position, with smaller diameter implants needing more space for soft-tissue development and tissue contouring.

IMPLANT ANGULATION

Implant angulation is particularly important in treatment planning for screw-retained restorations. Implants angled too far labially compromise the placement of the restorative screw, leaving the clinician with fewer restorative options. Implants angled too far lingually can result in unhygienic and unesthetic prosthetic design. For every millimeter of lingual inclination, the implant should be placed an additional millimeter apically in order to create an optimal emergence profile.14 In general, implant angulation should mimic angulation of adjacent teeth so long as they are in reasonable alignment (Fig. 4). Furthermore, maxillary anterior regions require a subtle palatal angulation to increase labial soft tissue bulk.15

INCLUSIVE TOOTH REPLACEMENT SOLUTION

The Inclusive® Tooth Replacement Solution was developed by Glidewell Laboratories as a complete, prosthetically driven method of restoring missing dentition. The solution comprises treatment planning, implant placement, patient-specific temporization, and the definitive restoration (Figs. 5a, 5b, 5c, 5d, 5e, 5f). When utilizing the comprehensive range of Inclusive Digital Treatment Planning services for guided implant surgeries and restorations, the clinician has absolute and precise control of each step. This results in an efficient and accurate workflow that is beneficial for the clinician and, ultimately, the patient. With the Inclusive Tooth Replacement Solution, the clinician has control of the four dimensions of implant placement in the esthetic zone, creating a consistently predictable result. Having a single source of services and materials is also advantageous in providing a more affordable yet high-value product for patients.

REFERENCES

  1. Albrektsson T, Brånemark PI, Hansson HA, Lindstrom J. Osseointegrated titanium implants. Requirements for ensuring a long-lasting, direct bone-to-bone implant anchorage in man. Acta Orthop Scand. 1981;52(2):155-70.
  2. Hounsfield GN. Computerized transverse axial scanning (tomography): Part I. Description of system. Br J Radiol .1973;46:1016-22.
  3. Al-Sabbagh M. Implants in the esthetic zone. Dent Clin N Am. 2006 Jul;50(3): 391-407.
  4. Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest. J Periodontol. 2000 Apr;71(4):546-49.
  5. Spray JR, Black CG, Morris HF, Ochi S. The influence of bone thickness on facial marginal bone response: stage 1 placement through stage 2 uncovering. Ann Periodontol. 2000 Dec;5(1):119-28.
  6. Saadoun AP, LeGall M, Touati B. Selection and ideal tridimensional implant posi- tion for soft tissue aesthetics. Pract Periodontics Aesthet Dent. 1999 Nov-Dec; 11(9):1063-72.
  7. Degidi M, Perrotti V, Shibli JA, Novaes AB, Piatelli A, Lezzi G. Equicrestal and subcrestal dental implants: a histologic and histomorphometric evaluation of nine retrieved human implants. J Periodontol. 2011 May;82(5):708-15. Epub 2010 Dec 7.
  8. Hermann JS, Buser D, Schenk RK, Schoolfield JD, Cochran DL. Biological width around one- and two-piece titanium implants. Clin Oral Implants Res. 2001 Dec; 12(6):559-71.
  9. Kazor CE, Al-Shammari K, Sarment DP, Misch CE, Wang HL. Implant plastic surgery: a review and rationale. J Oral Implantol. 2004;30(4):240-54.
  10. Berglundh T, Lindhe J. Dimension of the periimplant mucosa. Biological width revisited. J Clin Periodontol. 1996 Oct;23(10):971-73.
  11. Hermann F, Lerner H, Palti A. Factors influencing the preservation of the periimplant marginal bone. Implant Dent. 2007 Jun;16(2):165-75.
  12. Broggini N, McManus LM, Hermann JS, Medina RK, Buser D, Cochran DL. Peri-implant inflammation defined by the implant-abutment interface. J Dent Res. 2006 May;85(5):473-78.
  13. Saadoun AP, LeGall M, Touati B. Selection and ideal tridimensional implant position for soft tissue aesthetics. Pract Periodontics Aesthet Dent. 1999 Nov-Dec;11(9):1063-72.
  14. Potashnick SR. Soft tissue modeling for the esthetic single-tooth implant resto- ration. J Esthet Dent. 1998;10(3):121-31.
  15. Tishler M. Dental implants in the esthetic zone. Considerations for form and function. N Y State Dent J. 2004 Mar;70(3):22-6.

Course Objectives (2 CE Credits)

Proper implant positioning is patient- and often implant-specific, making prosthetic treatment planning and pre-placement protocol paramount for achieving predictable restorative results. Dr. Siamak Abai, staff dentist of clinical research at Glidewell Laboratories, details some of the established parameters with regard to implant spacing and angulation, and highlights the use of advanced tools such as Inclusive® Digital Treatment Planning services and the Inclusive® Tooth Replacement Solution to execute precise control over each individual case. Concepts include:
  • Patient-specific treatment planning
  • Mesiodistal orientation criteria
  • Labiolingual orientation criteria
  • Apico-coronal orientation criteria
  • Angulation considerations
  • Advantages of the Inclusive Tooth Replacement Solution

CE Summary

Since the advent of modern root form osseointegrated implant dentistry in 1952 by Per-Ingvar Brånemark and colleagues, clinicians have strived for improvements in implant positioning in the esthetic zone to achieve predictable restorative and esthetic results. Years of clinical experience in congruence with controlled clinical studies have led to established parameters as a guide for these results. Along with prosthetic treatment planning specific to each patient, adherence to these parameters can help maximize the chances of long-term success.

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