|Year : 2014 | Volume
| Issue : 2 | Page : 66-70
Short implants: A new dimension in rehabilitation of atrophic maxilla and mandible
Sanath Shetty, Naushad Puthukkat, S Vidya Bhat, K Kamalakanth Shenoy
Department of Prosthodontics, Yenepoya Dental College, Mangalore, Karnataka, India
|Date of Web Publication||15-Oct-2014|
Department of Prosthodontics, Yenepoya Dental College, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Insufficient alveolar bone height is a common clinical situation encountered more in the posterior jaws. Advanced surgical procedures such as bone grafting, sinus lifting, and nerve repositioning are required to overcome this condition and make implant treatment possible for such patients. Prolonged healing period, increased morbidity, and longer duration of the implant treatment accompanies these procedures. Short implants are considered as a viable alternative in patients with reduced alveolar bone height to avoid more invasive surgical procedures. They simplify the implant treatment, reduce patient morbidity, shorten the duration of treatment, and make it less expensive. In the past, when machined implants were used, rehabilitation with short implants showed increased failure rate in comparison to longer implants. With the improvements in the surface topography of implants, which increase the bone implant contact, and use of adapted surgical protocols similar survival rates as that of regular implants have been reported even with short implants. Various methods to increase the functional surface area and decrease the stress on the prosthesis have greatly contributed to the increased success rate of short implants.
Clinical Relevance to Interdisciplinary Dentistry
- Successful outcome of implant treatment depends on the coordinated efforts of various specialties
- Proper technique of implant placement by the surgeon and prior planning of the prosthesis by the prosthodontist is essential
- Maintenance and periodic evaluation of periodontal health are necessary.
Keywords: Bone grafting, bone implant contact, functional surface area, short implants, surface topography
|How to cite this article:|
Shetty S, Puthukkat N, Bhat S V, Shenoy K K. Short implants: A new dimension in rehabilitation of atrophic maxilla and mandible. J Interdiscip Dentistry 2014;4:66-70
|How to cite this URL:|
Shetty S, Puthukkat N, Bhat S V, Shenoy K K. Short implants: A new dimension in rehabilitation of atrophic maxilla and mandible. J Interdiscip Dentistry [serial online] 2014 [cited 2021 Sep 18];4:66-70. Available from: https://www.jidonline.com/text.asp?2014/4/2/66/142935
| Introduction|| |
Implant treatment becomes more challenging to the clinicians and more enduring to the patients when the alveolar bone height is insufficient. The condition is more common in the posterior jaws due to the resorption of alveolar bone and pneumatization of the maxillary sinus. Advanced surgical procedures are required to overcome this clinical situation and make implant treatment possible for such patients. These ancillary procedures like ridge augmentation or sinus grafting with simultaneous implant placement has shown more intra and postoperative complications.  Prolonged healing period, increased morbidity, and longer duration of the implant treatment accompanies these procedures. The expertise of a specialist surgeon is required to perform these surgeries.
As far as possible, rehabilitation with implants should be simple, cost effective, highly predictable, and of shorter duration. Short implants are considered as a viable alternative in patients with reduced alveolar bone height to avoid more invasive surgical procedures. ,, They simplify the implant treatment, reduce patient morbidity, shorten the duration of treatment, and make it less expensive. In the past, when machined implants were used, rehabilitation with short implants showed increased failure rate in comparison to longer implants. With the improvements in the surface topography of implants and use of adapted surgical protocols similar survival rates as that of regular implants have been reported even with short implants. [5 ]
| Scientific rationale for short implants|| |
When stress is applied to the natural tooth, it is distributed in to the underlying bone along the entire root length due to the presence of periodontal ligaments as the tooth tends to pivot around the center of the root. However in case of implants, where periodontal ligament is absent, the greatest magnitude of stress concentration is seen at the crest which tapers apically up to 5 mm from the crest. Stress concentration in the apical region is much less.  Most endosteal dental implants are fabricated from alloyed or pure titanium with a modulus of elasticity (stiffness) approximately 5 times greater than dense cortical bone. A basic mechanical principle states that when two materials of different moduli of elasticity are placed together with no intervening material and one is loaded, the stress concentration can be observed where the two materials first come into contact.  These stress contours form a v-shaped or u-shaped pattern, with greater magnitude near the point of first contact, which corresponds to the crest of the bone.  The phenomenon of higher crestal stresses next to the implant is confirmed in photoelastic and two-dimensional or three-dimensional finite element analysis (FEA) studies when an implant is placed within a bone simulant and loaded [Figure 1]. ,
|Figure 1: Finite element analysis model showing the V-shaped stress pattern in the crestal 5 mm of implant body|
Click here to view
Increase in implant length will increase the total surface area of the implant and improve the primary stability by increasing the bone implant contact (BIC). But the area that transfers the compressive and tensile loads to bone that is, functional surface area (FSA) is confined to the crestal 5-7 mm. Increasing the length of the implant will not change this where as a short implant with a wider diameter provides both, improved primary stability and increased FSA. 
How short is short?
There is no consensus in the literature on the definition of a short implant. Various authors have used different lengths of implants as short implants. Earlier studies considered 10 mm as standard length for implants and anything less than that as short implants. Renouard and Nisand defined short implants as an implant with a designed intra bony length of 8 mm or less.  6 th European consensus conference of European Association of Dental Implantologists in 2011 approved the classification of implants given by Olate et al., which states, implants are usually referred to as short if their length measures <8 mm, 9-13 mm in length as a medium and long implants are usually understood to be over 13 mm in length. 
Merits of short implants
The main advantage of using short implants is that it simplifies the implant surgery by avoiding the more invasive procedures like bone grafting, sinus lifting, nerve repositioning, etc., and thus decreases morbidity and reduces the healing period. Advanced imaging modalities may not be required which will reduce the radiation exposure. Patient acceptance will be more as it avoids the need for complicated surgeries, reduces the duration of treatment period and cost.
Reduction of the implant surface area is one of the presumed reasons for the lower survival rate of short implants which will lead to less bone to implant contact after osseointegration. The functional forces after loading will be transferred to the crestal bone through this reduced surface of force distribution, which will lead to crestal bone loss. Compromised crown to implant the ratio is thought to be another problem, which will affect the success of the treatment. The poor quality of bone in the posterior region, especially in the maxilla, where short implants are mostly used is another contributing factor.
Earlier clinical trials have shown conflicting reports regarding the treatment outcome and long-term survival of short implants. However recent clinical trials have shown that success rate of short implants is comparable with that of regular implants. ,, This difference was due to the various methods they adopted to overcome the abovementioned shortcomings of the short implants. This includes modification of implant characteristics and biomechanical considerations for stress reduction.
Increasing the diameter of the implant is an effective method to increase the implant surface area. Wider diameter short implants will have increased FSA and improved primary stability. It allows engagement of a maximal amount of bone and better distribution of stress in the surrounding bone. An increase in the diameter reduces stress at the implant neck and is associated with good distribution of force compared with increases in implant length.  Implant strength and fracture resistance can be improved by increasing the diameter of the implant. Wider implants also facilitate the creation of a better emergence profile, especially in the posterior segment. An increase in diameter by 1 mm will increase the surface area by 30-200% depending on the implant design.  A three-dimensional FEA demonstrated that increasing the implant diameter resulted in a 3.5-fold reduction in crestal strain, whereas increasing the implant length resulted in only 1.65-fold reduction in crestal strain.  In natural dentition, molars are subjected to high occlusal forces and the root surface area of molars is 200% more than that of other teeth. This is achieved by increasing the diameter, change in the design, increasing the number, and splinting of the roots, but not by increasing the length of the roots. Similar approach is logical for short implants. If wider implant cannot be placed, each molar can be supported with 2 short implants, thereby increasing the FSA.
Most of the earlier studies using short implants showed less favorable results as compared to longer implants because of the use of machined surface implants. Studies conducted using rough surface implants showed similar survival rates for both the types. The fact that alteration of the implant surface can influence the success of osseointegration has been proven in various studies. ,, This can be achieved by either subtractive processes like blasting, etching and oxidation, or additive processes like titanium plasma spraying, hydroxyapatite and other calcium phosphate coating and ion deposition. Rough implants offer extensive area for osseointegration. It increases the BIC and FSA in addition to improve the wettability of the implant surface.
Photofunctionalization of implants
Treatment of implants with ultraviolet (UV) light has been found to increase the BIC from 55% to near maximum level of 98.2%. This resulted in 3-fold increase in the strength of osseointegration. ,, This increase is attributed to the generation of superhydrophilicity, a significant decrease in surface hydrocarbons, and improvement in the electrostatic status of titanium surfaces after UV treatment. The biological effects along with UV-enhanced surface properties are collectively defined as photofunctionalization of titanium implants. An animal study showed implants with 40% shorter length resulted in a 50% or more decrease in the strength of osseointegration, but after photofunctionalization, the osseointegration strength doubled and the disadvantage of short implants was eliminated.  A recent human study has demonstrated the effectiveness of photofunctionalization in complex cases using short implants with lesser diameter.  It allows for the placement of short implants in the alveolar ridges which are not wide enough to allow the placement of larger diameter implants.
Macro geometric design
Increasing the diameter is a logical option for increasing the surface area of short implants. But there is an anatomical limit to how much the diameter can be increased. Modifications in the macro geometry of the implant are advantageous in providing more area for BIC and FSA. Various thread shapes such as square, v-shaped, and reverse buttress are available for implants of which square threads provide more surface area for a given length of the implant. Increasing the number of threads per unit area (decreased thread pitch) and increasing the thread depth also enhance the FSA of short implants.[Figure 2]
Bone density is directly proportional to its strength. Less dense bone may demonstrate a reduction of its strength by 50-80% compared to higher density bone. Poor bone quality is strongly linked to higher failure rates in implants.  Increased failure rates of short implants in the early trials were attributed to the use of machined implants in poor quality bone, especially in the posterior maxilla. This negative effect is somewhat dampened by rough surfaced implants now. Use of self-tapped implants has also brought down the failure rates.  Use of bone expanders/condensers during osteotomy procedure also improves the bone density and there by increases the success of a short implant.  A two-stage implant placement approach was suggested by Gentile et al. while using short implants as it was associated with higher success rates.  But there are other studies which shows no statistical significant differences in the success rate between single stage and two stage protocols.  However, some authors have recommended a two-stage approach with submerged implants for completely edentulous arches. 
Crown implant ratio
A consensus conference defined a desirable crown height space for a fixed prosthesis to be between 8 and 12 mm (bone level to opposing dentition).  This height leaves 3 mm for soft tissue (includes biologic width and soft tissue coverage of implant collar), 2 mm for an occlusal porcelain, and an abutment 5mm high. Increased height of the prosthesis increases the risk of component and material fracture due to elevated forces on the restoration. Therefore, increased crown height has to be considered as a factor that can affect clinical outcomes both technically and biologically.
Increased crown implant ratio (CIR) is a major concern with short implants. A 1:1.5 crown root ratio is suggested as most favorable and 1:1 as a minimum for a tooth abutment.  But the same need not be applicable for short implants and the ideal CIR has not been established. Various studies have demonstrated high success rates with a CIR of up to 2 and increased CIR did not result in additional peri-implant bone loss. ,, This was possible by giving due considerations for various stress reduction methods like avoiding lateral loads, cantilevers, etc.
Biomechanical methods for stress reduction
Biomechanical methods to decrease the stresses to short implants are a critical factor in deciding the success of the treatment. These include decreasing force to the implant prosthesis and increasing implant surface area of prosthesis support.
By avoiding lateral contacts in mandibular excursions and eliminating cantilevers, detrimental forces to which implant prosthesis is subjected can be reduced. The occlusal height of the crown should not affect the force moment along the vertical axis, because if it is centered, its effective moment arm is nonexistent.  Apart from increasing the diameter and surface area, increasing the number of implants and splinting them together can increase the area of forces applied to the prosthesis.
| Conclusion|| |
Insufficient alveolar bone height for implant placement is a commonly seen problem in the posterior jaws. Traditional way of overcoming this difficulty is by undergoing adjunctive surgical procedures. Though they are proven to be successful, these procedures result in delayed healing, increased morbidity, and prolonged treatment period. Short dental implants have been successfully used in such situations with comparable survival rates with that of longer implants. Various methods to increase the surface area and BIC along with the stress reduction to the implant prosthesis have made short implants a viable and more predictable alternative to advanced surgical interventions.
| References|| |
|1.||Esposito M, Cannizzaro G, Soardi E, Pistilli R, Piattelli M, Corvino V, et al. Posterior atrophic jaws rehabilitated with prostheses supported by 6 mm-long, 4 mm-wide implants or by longer implants in augmented bone. Preliminary results from a pilot randomised controlled trial. Eur J Oral Implantol 2012;5:19-33. |
|2.||Fugazzotto PA. Shorter implants in clinical practice: Rationale and treatment results. Int J Oral Maxillofac Implants 2008;23:487-96. |
|3.||Annibali S, Cristalli MP, Dell'Aquila D, Bignozzi I, La Monaca G, Pilloni A. Short dental implants: A systematic review. J Dent Res 2012;91:25-32. |
|4.||Lai HC, Si MS, Zhuang LF, Shen H, Liu YL, Wismeijer D. Long-term outcomes of short dental implants supporting single crowns in posterior region: A clinical retrospective study of 5-10 years. Clin Oral Implants Res 2013;24:230-7. |
|5.||Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17 Suppl 2:35-51. |
|6.||Lum LB. A biomechanical rationale for the use of short implants. J Oral Implantol 1991;17:126-31. |
|7.||Von Recum A, editor. Handbook of Biomaterials Evaluation: Scientific, Technical and Clinical Testing of Implant Materials. New York, NY: MacMillian; 1986. |
|8.||Shigley JE, Mischke CR. Mechanical Engineering Design. 5 th ed. New York, NY: McGraw-Hill; 1989. p. 325-70. |
|9.||Bidez MW, Misch CE. Issues in bone mechanics related to oral implants. Implant Dent 1992;1:289-94. |
|10.||Sevimay M, Turhan F, Kiliçarslan MA, Eskitascioglu G. Three-dimensional finite element analysis of the effect of different bone quality on stress distribution in an implant-supported crown. J Prosthet Dent 2005;93:227-34. |
|11.||Misch CE. Implant design considerations for the posterior regions of the mouth. Implant Dent 1999;8:376-86. |
|12.||Olate S, Lyrio MC, de Moraes M, Mazzonetto R, Moreira RW. Influence of diameter and length of implant on early dental implant failure. J Oral Maxillofac Surg 2010;68:414-9. |
|13.||Kotsovilis S, Fourmousis I, Karoussis IK, Bamia C. A systematic review and meta-analysis on the effect of implant length on the survival of rough-surface dental implants. J Periodontol 2009;80:1700-18. |
|14.||Romeo E, Bivio A, Mosca D, Scanferla M, Ghisolfi M, Storelli S. The use of short dental implants in clinical practice: Literature review. Minerva Stomatol 2010;59:23-31. |
|15.||Misch CE, Steignga J, Barboza E, Misch-Dietsh F, Cianciola LJ, Kazor C. Short dental implants in posterior partial edentulism: A multicenter retrospective 6-year case series study. J Periodontol 2006;77:1340-7. |
|16.||Himmlová L, Dostálová T, Kácovský A, Konvicková S. Influence of implant length and diameter on stress distribution: A finite element analysis. J Prosthet Dent 2004;91:20-5. |
|17.||Misch CE, Bidez MW. Contemporary Implant Dentistry. 2 nd ed.St. Louis: Mosby; 1999. |
|18.||Petrie CS, Williams JL. Comparative evaluation of implant designs: Influence of diameter, length, and taper on strains in the alveolar crest. A three-dimensional finite-element analysis. Clin Oral Implants Res 2005;16:486-94. |
|19.||Buser D, Schenk RK, Steinemann S, Fiorellini JP, Fox CH, Stich H. Influence of surface characteristics on bone integration of titanium implants. A histomorphometric study in miniature pigs. J Biomed Mater Res 1991;25:889-902. |
|20.||Smith DC, Pilliar RM, Chernecky R. Dental implant materials. I. Some effects of preparative procedures on surface topography. J Biomed Mater Res 1991;25:1045-68. |
|21.||Pilliar RM. Overview of surface variability of metallic endosseous dental implants: Textured and porous surface-structured designs. Implant Dent 1998;7:305-14. |
|22.||Aita H, Hori N, Takeuchi M, Suzuki T, Yamada M, Anpo M, et al. The effect of ultraviolet functionalization of titanium on integration with bone. Biomaterials 2009;30:1015-25. |
|23.||Ogawa T. UV photofunctionalization of titanium implants. J Craniofac Tissue Eng 2012;2:151-8. |
|24.||Att W, Ogawa T. Biological aging of implant surfaces and their restoration with ultraviolet light treatment: A novel understanding of osseointegration. Int J Oral Maxillofac Implants 2012;27:753-61. |
|25.||Ueno T, Yamada M, Hori N, Suzuki T, Ogawa T. Effect of ultraviolet photoactivation of titanium on osseointegration in a rat model. Int J Oral Maxillofac Implants 2010;25:287-94. |
|26.||Funato A, Yamada M, Ogawa T. Success rate, healing time, and implant stability of photofunctionalized dental implants. Int J Oral Maxillofac Implants 2013;28:1261-71. |
|27.||Misch CE. Bone density: A key determinant for clinical success. In: Misch CE, editor. Contemporary Implant Dentistry. St. Louis: The CV Mosby Company; 1999. p. 109-18. |
|28.||Martinez H, Davarpanah M, Missika P, Celletti R, Lazzara R. Optimal implant stabilization in low density bone. Clin Oral Implants Res 2001;12:423-32. |
|29.||Gentile MA, Chuang SK, Dodson TB. Survival estimates and risk factors for failure with 6×5.7-mm implants. Int J Oral Maxillofac Implants 2005;20:930-7. |
|30.||Sun HL, Huang C, Wu YR, Shi B. Failure rates of short (=10 mm) dental implants and factors influencing their failure: A systematic review. Int J Oral Maxillofac Implants 2011;26:816-25. |
|31.||Esposito M, Grusovin MG, Chew YS, Coulthard P, Worthington HV. One-stage versus two-stage implant placement. A Cochrane systematic review of randomised controlled clinical trials. Eur J Oral Implantol 2009;2:91-9. |
|32.||Misch CE, Goodacre CJ, Finley JM, Misch CM, Marinbach M, Dabrowsky T,et al. Consensus conference panel report: Crown-height space guidelines for implant dentistry-part 2. Implant Dent 2006;15:113-21. |
|33.||Shillingburg HT Jr, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of Fixed Prosthodontics. 3 rd ed. Chicago, IL: Quintessence Publishing; 1997. p. 89-90. |
|34.||Blanes RJ, Bernard JP, Blanes ZM, Belser UC. A 10-year prospective study of ITI dental implants placed in the posterior region. II: Influence of the crown-to-implant ratio and different prosthetic treatment modalities on crestal bone loss. Clin Oral Implants Res 2007;18:707-14. |
|35.||Rokni S, Todescan R, Watson P, Pharoah M, Adegbembo AO, Deporter D. An assessment of crown-to-root ratios with short sintered porous-surfaced implants supporting prostheses in partially edentulous patients. Int J Oral Maxillofac Implants 2005;20:69-76. |
|36.||Schulte J, Flores AM, Weed M. Crown-to-implant ratios of single tooth implant-supported restorations. J Prosthet Dent 2007;98:1-5. |
|37.||Bidez MW, Misch CE. Biomechanics. In: Misch CE, editor. Contemporary Implant Dentistry. 3 rd ed. St. Louis, MO: Mosby; 2008. p. 557-98. |
[Figure 1], [Figure 2]