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Abstract

This study proposes a brief literature review on the current condition of implant dentistry with regard to rehabilitation of prosthetic osseointegrated implants. At this stage, manufacturers of implants and prosthetic components have provided a number of innovative options for dental surgeons with promises of high performance and predictability. However, it is known that the established concepts and biological conditions such as osseointegration parameters, surface treatment, implant design, and early and immediate loading are difficult to be changed. This scientific basis is increasingly necessary for the update of professionals who are active in the academic or clinical areas in order to provide the best quality of treatment to patients and consequent quality of life.

Key words

 prosthetic rehabilitation, implant-supported, biomechanics, loading

Summary of pertinent research

The need to replace missing teeth with the purpose of reestablishing proper dental function has been a common concern since the earliest civilizations. One option which has been tested throughout history is dental implants. Several metal alloys and surgical methods, and different types of implants (i.e., needle, bone-supported, blade implant) have been tested with little success [1-3]. During the 1960s and 1970s, Swedish physician Per Ingvar Bränemark published the results of his research showing the osseointegration of titanium implants and established the principles of their use in dentistry, reason why he is known as “the father of implant dentistry”[3,4] Initially, Ingvar’s contemporaries within the Swedish dental community were skeptical of his work. This, however, may have ultimately contributed to the success of modern dental implants. One consequence of this skepticism was the development of strict laboratory and clinical research parameters (i.e., the Bränemark protocols). Therefore, when the global dental scientific community was introduced to Bränemark’s research, it had already been verified with clinical and longitudinal monitoring, material-related protocols, components, surgical and prosthetic techniques [5].

Using his work as a foundation, other scientists have tried to innovate dental implants by investigating the use of new implant materials, new implant designs, new external treatments, and novel surgical techniques [6,7]. Many also attempted to understand patient’s systemic conditions, thereby hoping to reduce osseointegration time and extend the clinical application of implants without reducing the benchmarked success rate of the Bränemark protocols.

With regard to prosthetics, the successful translation of previously established knowledge into functional dental prostheses has been rapidly investigated. The main research focused on establishing protocols that would develop the ideal prosthetic plan for each clinical case [1,2,8,9]. Thus, studies on the rehabilitation of partially edentulous patients, using single and multiple prostheses, as well as the development of overdentures attached to the implant, were being developed [1,2,10,11]. Research emerged in the following areas: cemented prostheses, retention and connection of the prostheses to implants, development of new prosthetic abutments, biomechanical studies, tooth and implant connections, force distribution in patients wearing removable prostheses, studies of implant materials, and application of previous clinical and laboratorial techniques only used in conventional prostheses [12]. Special attention was given to occlusal aspects since the prosthesis attached to the implant transmitted compressive and shear occlusal forces to the bone when contrasted to the tooth traction force, which transferred to the bone in a healthy occlusion [13,14].

The development and spreading of new techniques and commercial brands have made dental implants increasingly more affordable, which are often included in prosthetic planning. On the other hand, the range of possible applications of this treatment, even without scientific support, and the false sense of success despite correct surgical and prosthetic planning, has increased failures in this form of treatment [8]. The scientific community has been making an effort to determine the safety limits as to what extent dental implants may be used to attach dental prostheses and maintain a high success rate of this treatment.

Therapeutic approach

Indications

One step in rehabilitation using prostheses is the understanding of the differences among a range of treatment options using implants and conventional dental rehabilitation. When properly planned, both types of fixed prostheses (i.e., on the tooth or an implant) have excellent success rates and prognoses, either for fully removable or partially removable prostheses [15]. For this reason, success rate cannot be the only variable considered when deciding whether to replace an endodontically treated tooth with an implant—generally speaking, preserving the tooth with the attached periodontal ligament is always the preferred method [16,17]. However, in order to replace a missing tooth, local and systemic conditions must allow for sufficient potential benefit to the patient; the best treatment option is an implant-attached prosthesis [18].

With regard to adhesive prostheses, despite its superiority in preserving the dental structure compared to conventional fixed prostheses, they had lower associated success rates than restoring edentulous spaces with prostheses attached to implants and even conventional fixed bridges [15,16]. Adhesive prostheses should only be used as a secondary option in clinical situations where there is greater cost/benefit for patients with socioeconomic challenges.

The complication types also differ among prostheses. Based on a short-term analysis (two years), dental prostheses appear to have had better success rates [19]. Any problems associated with the prosthesis biomechanics may be mitigated by the periodontal ligament. However, due to the lack of complications associated with prosthetic implants (e.g., tooth decay, endodontic treatment, and dental sensitivity) the number of long-term complications associated with a tooth-fixed prosthesis was higher than those associated with a implant-fixed prosthesis [20]. Additionally, Albrektsson et al. (2012) found that technical complications occur more frequently with fixed prostheses than with single prostheses, thus proving that fixed prosthesis were safer [18].

Biomechanics

Another important aspect that has been studied was whether the type of implant prostheses influenced its success rate, referred to whether it caused pain, movement or inflammation of the peri-implant tissue, or increased bone resorption [21]. Some authors mentioned that there was no difference between the success rates of unitary prostheses or bridges attached to implant [22,23]. Studies have shown that unitary crowns were the most successful at preventing implant faults, followed by fixed prostheses (partially or totally), and overdentures; this was consistent with various other studies [19,24,25]. Salvi et al. stated that the number of implants that supported a fixed prosthesis was neither associated to an increase in mechanical and technical faults nor it affected the success rate of dental implants with regard to their durability [25]. However, fixed prostheses were also associated with a greater number of technical failures than unitary prostheses [18].

With regard to the implant-attached prosthesis design and its influence on treatment success, the tooth/support ratio was a valid consideration for prosthetics attached to teeth only. This was due to the fact that for prostheses attached to implants — regardless of their size or the bone density in the edentulous region — force distribution occurred in the most cervical region of the implant (the first 10 mm) as verified in the laboratory research using FEA (finite element analysis), extensometry, and photoelasticity analyses [19].

Consequently, there has been no clinical evidence whether this ratio reflected a higher or lower degree of peri-implant bone resorption [25,26]. The crown/implant ratio must always be calculated by associating the crown with a 10 mm implant, as this is the minimum accepted value. Therefore, some caution must be exercised when there is a larger interocclusal distance, regardless of implant length. An increase in the number of implants, a reduction in lever arms, an increase in the implant diameter and/or insertion of implants with a greater surface area (surface treated implants), the use of removable prostheses (lower retention and the transmission of the load is facilitated by the mucous support), the removal of prostheses prior to sleep, and combining implants may reduce the unbalanced distribution of forces transmitted to the bone via the implant. Wang et al. stated that reduction in the lever arm (reduction in the crown/implant ratio) would be of greater benefit to the peri-implant bone than an increase in the implant width [27].

Further studies must be performed in order to prove that these biomechanical conditions, which appear in the laboratory setting, could be applied to dental consultations. For instance, clinical instances of severely resorbed bone, associated with the reestablishment of the vertical dimension of occlusion (VDO), were a common clinical condition in prosthetic rehabilitation consultations. This was due the fact that this had been barely researched. The best option was to completely or partially re-establish VDO by reducing the prosthesis/implant ratio. Therefore, further clinical studies that focused on the biomechanical parameters are required to better understand the safety limits of this and other clinical situations. Similarly, another gap in clinical and laboratorial studies relates to abutment angulation.12 Although the laboratory research indicated a greater overload on the peri-implant bone and on the components fixing the prosthesis with angulated abutments (i.e., screws and cement lines), there was no clinical evidence in the literature to support such data. There was no direct association between abutment angulation and the survival rate of either prostheses or implants [25,28].

Moreover, systematic reviews also showed that there were no significant differences between the fixation techniques (i.e., screwed and cemented) used in fixed prostheses [25,28,29], despite the greater tendency for biological and mechanical complications in the cemented prostheses and screwed prostheses, respectively. One problem that was discovered when comparing the results of these types of prostheses was the lack of specific cementing protocols for this fixed prosthesis (for both the material and the technique used [30]. These studies stated that cemented prostheses, such as unitary prostheses and non-extended fixed bridges, had high success rates when properly used. For extended fixed bridges or cantilever prostheses, a screwed fixation would be more appropriate [27]. The main advantage of screwing in the prostheses was that they could be removed and replaced without damaging the structure of the prostheses or implants, thereby facilitating subsequent clinical procedures [12,29,30].

Another important aspect that has influenced prosthetic and implant use planning was the attachment of the implant to the tooth [31]. One previous study stated that fixed and unitary prostheses attached to the teeth or implant must be the first choice when using a cantilever prosthesis, an adhesive prosthesis, or a prostheses joining the tooth with the implant [31]. Thus, it is recommended that this clinical situation is avoided whenever possible. However, provided that the prosthesis and abutments (tooth and implant) were satisfactory, there was no reason not to use either method when others are not applicable to the patient.

Restorative materials

With regard to the material used for prosthetic rehabilitation, there was lack of evidence to verify the success rate of prostheses and implants when using different restorative materials [21,32-34] gold, titanium, and zirconium, among others, exhibited better biocompatibility than alternative alloys (i.e.., Ni-Cr and Co-Cr) [35].

Regarding the methods used to create the implant infrastructure, one previous study stated that there was no better technique than CAD/CAM [36]. However, some authors recommended the use of CAD/CAM, either with metal (titanium) or ceramic (zirconia), only for patients who needed highly individualized abutments and for dentists/laboratories with a high level of experience with this technique. This was due to the pre-made components which must be properly adaptable to the single implant platforms [21,32,34].

Functional loading x Prosthetic design

For the planning of prostheses attached to implants, what researchers studied most was the required time for the functional loading of implants [13]. Hence, time-related terms such as immediate loading, premature loading, and conventional loading (referring to the protocols established by Bränemark) were common topics at conferences and symposia in this field. The search for high success rates of osseointegration for implants associated with predictable results from a prosthetic/surgical point-of-view, with regard to the immediate or premature loading of implants, have given rise to various studies that investigated different surgical techniques, modifications in the design and area of implants, and the planning of prostheses [13,37-41].

Some authors found that there was no significant difference between immediate, premature, and conventional loading, despite the latter’s success rate which was consistent with the results of a previous study performed by Esposito et al. in 2008 [42-44]. However, it was discovered that the comparison could not be made due to the differences in location, technique, and implants used in both studies [42]. Consequently, some authors made recommendations based on systematic revisions by assessing the type of prosthetic rehabilitation. For protocol prostheses, both immediate and premature load are viable for the maxilla and mandible [21]. In contrast, for overdentures, immediate and premature loading have not been well documented for the maxilla and it should only be used in the mandible [21,42].

For partially edentulous individuals, in the esthetic region (anterior maxilla), authors disagreed with the previously mentioned applications [28]. Many of them still believed that immediate and premature loading could be used in this region when no risk factors are involved. However, Atieh et al. stated that conventional loading was statistically better and that one should only alter this protocol in cases selected by a dentist with minimum specific knowledge and technical skills [46].

Similarly, implants in the posterior region of the mandible that were subject to immediate or premature loading may be used under the same criteria, although further studies are required to establish a safe protocol for different load applications [28,47]. For the posterior region of the maxilla, in 2009, Weber et al. stated that premature loading was the most viable alternative to speed up the six-month period suggested by the Bränemark protocol [28].

However, Roccuzzo stated that there were still no well-defined protocols which confirmed the preferred use of immediate or premature loading over conventional loading; many studies proposed criteria where premature or immediate loading would be contraindicated [48]. In clinical situations, such as bruxism or surgical sites with fresh alveoli or those subject to guided bone regeneration, short implants, and implants without primary stability, immediate or premature loading should follow the waiting time established by the initial protocol for osseointegration. In addition, the surgical technique, type of implant, and surface treatment may have influenced the success rate when immediate or premature loading was used [28,43,46,47]. Atieh et al. recommended that the implant should have the largest diameter possible so that the prosthesis may be screwed without being in contact with the maximum intercuspation and in excursive movements [46].

Clinical procedures

After appropriate prosthetic planning and surgical execution during the implantation of prostheses, some clinical steps may still compromise biomechanical and esthetic results of the prosthesis. Therefore, the selection of materials, molding techniques, and the esthetic manipulation of supporting tissues were important steps that need to be observed.

With regard to the main molding applied techniques, it is stated that the joining of transferents, prior to molding, increased the reliability of the model and favored a more passive prosthesis positioning.49 As of the transfer, for clinical cases in which a reduced number of implants was required < 3), there was no difference between open or closed molding. In situations where the prosthesis would be replaced by four or more implants, the open molding technique was statistically better [49]. As for the mold material, there was no difference in performance between silicon and polyester [49]. Pita et al. found that internally connected implants were more stable upon insertion and thereby facilitated molding and connection [50].

In reference to the manipulation or remodeling of gum tissue resulting from prolonged use of temporary prostheses, there is little clinical evidence in the literature about associating clinical manipulation with implant prostheses, despite being a commonly used procedure in clinical prosthetics. Factors that included the distance between the implants or between the teeth and the implant, thickness of the buccal bone plate, and gum health were factors that positively contributed to prosthetic treatment for esthetic purposes [51,52]. Using ‘switching’ platform or Cone Morse abutments also helped preserving the height of the peri-implant bone crest and promoted thicker connective tissue around the implant [35,50,53].

Conclusion

Research studies referencing mechanical and biological failures often occur when clinical and laboratorial criteria are not synchronized when the implant prosthess installation. The limits for the application of these techniques are gradually changing as implants and surgical methods develop and evolve. Continuous technical and scientific improvement by medical professionals who perform clinical procedures and technicians who perform laboratory procedures should be pursued in order to extend the life of implants and rehabilitation treatment success rates.

References

1. Roach M (2007) Base metal alloys used for dental restorations and implants. Dent Clin North Am 51: 603-627. [Crossref]
2. Wataha JC (1996) Materials for endosseous dental implants. J Oral Rehabil 23: 79-90. [Crossref]
3. Gaviria L, Salcido JP, Guda T, Ong JL (2014) Current trends in dental implants. J Korean Assoc Oral Maxillofac Surg 40: 50-60. [Crossref]
4. Brånemark PI (1965) Capillary form and function. The microcirculation of granulation tissue. Bibl Anat 7: 9-28. [Crossref]
5. Carl M (2008) Implantes dentais contemporâneos. Rio de Janeiro: Elsevier
6. Triplett RG, Frohberg U, Sykaras N, Woody RD (2003) Implant Materials, Design, and Surface Topographies: Their Influence on Osseointegration of Dental Implants. J Long Term Eff Med Implants 13: 485-501. [Crossref]
7. Lee JH, Frias V, Lee KW, Wright RF (2005) Effect of implant size and shape on implant success rates: a literature review. J Prosthet Dent 94: 377-381. [Crossref]
8. Henry PJ (2000) Tooth loss and implant replacement. Aust Dent J 45: 150-172. [Crossref]
9. Bartlett D (2007) Implants for life? A critical review of implant-supported restorations. J Dent 35: 768-772. [Crossref]
10. MacEntee MI, Walton2021 Copyright OAT. All rights reservdentures and implant-related services: a framework for analysis and preliminary outcomes. J Prosthet Dent 79: 24-30. [Crossref]
11. Carlsson GE (2014) Implant and root supported overdentures - a literature review and some data on bone loss in edentulous jaws. J Adv Prosthodont 6: 245-252. [Crossref]

1. Chaar MS, Att W, Strub JR (2011) Prosthetic outcome of cement- retained implant- supported fixed dental restoration: a systematic review. J Oral Rehabil 38: 697-711. [Crossref]
2. Sahin S, Cehreli MC, Yalçin E (2002) The influence of functional forces on the biomechanics of implant-supported prostheses--a review. J Dent 30: 271-282. [Crossref]
3. Cehreli M, Sahin S, Akca K (2004) Role of mechanical environment and implant design on bone tissue differentiation: current knowledge and future contexts. J Dent 32: 123-32. [Crossref]
4. Salinas TJ, Eckert SE (2007) In patients requiring single-tooth replacement, what are the outcomes of implant- as compared to tooth-supported restorations? Int J Oral Maxillofac Implants 22: 71-95. [Crossref]
5. Iqbal MK, Kim S (2007) For teeth requiring endodontic treatment, what are the differences in outcomes of restored endodontically treated teeth compared to implant-supported restorations? Int J Oral Maxillofac Implants 22: 96-116. [Crossref]
6. Torabinejad M, Anderson P, Bader J, Brown LJ, Chen LH, et al. (2007) Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review. J Prost Dent 98: 285-311. [Crossref]
7. Albrektsson T, Donos N (2012) Implant survival and complications. The Third EAO consensus conference 2012. Clin Oral Implants Res 23: 63-65. [Crossref]
8. Misch CE, Goodacre CJ, Finley JM, Misch CM, Marinbach M, et al. (2005) Consensus conference panel report: crown-height space guidelines for implant dentistry-part 1. Implant Dent 14: 312-318. [Crossref]
9. Wennerberg A, Albrektsson T (2011) Current challenges in successful rehabilitation with oral implants. J Oral Rehabil 38: 286-294. [Crossref]
10. Weber HP, Sukotjo C (2007) Does the type of implant prosthesis affect outcomes in the partially edentulous patient? Int J Oral Maxillofac Implants 22 Suppl: 140-172. [Crossref]
11. Ericsson I, Lekholm U, Branemark PI, Lindhe J, Glantz PO, et al. (1986) clinical evaluation of fixed-bridge restorations supported by the combination of teeth and osseointegrated titanium implants. J Clin Periodontol 13: 307-12. [Crossref]
12. Steenberghe V (1986) A retrospective multicenter evaluation of the survival rate of osseointegrated fixtures supporting fixed partial prostheses in the treatment of partial edentulism. J Prosthet Dent 61: 217-23. [Crossref]
13. Lindh T, Gunne J, Tillberg A, Molin M (1998) A meta-analysis of implants in partial edentulism. Clin Oral Implants Res 9: 80-90. [Crossref]
14. Salvi GE, Brägger U (2009) Mechanical and t echnical risks in implant therapy. Int J Oral Maxillofac Implants 24 Suppl: 69-85. [Crossref]
15. Blanes RJ (2009) To what extent does the crown-implant ratio affect the survival and complications of implant-supported reconstructions? A systematic review. Clin Oral Implant Res 20: 67-72. [Crossref]
16. Wang TM, Leu LJ, Wang J, Lin LD (2002) Effects of prosthesis materials and prosthesis splinting on peri-implant bone stress around implants in poor-quality bone: a numeric analysis. Int J Oral Maxillofac Implants 17: 231-7. [Crossref]
17. Weber HP, Morton D, Gallucci GO, Roccuzzo M, Cordaro L, et al. (2009) Consensus statements and recommended clinical procedures regarding loading protocols. Int J Oral Maxillofac Implants 24: 180-183. [Crossref]
18. Sailer I, Muhlemann S, Zwahlen M, Hammerle CH, Schneider D (2012) Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin Oral Implant Res 23: 163-201. [Crossref]
19. Chaar MS, Att W, Strub JR (2011) Prosthetic outcome of cement-retained implant-supported fixed dental restorations: a systematic review. J Oral Rehabil 38: 697-711. [Crossref]
20. Pjetursson BE, Zwahlen M, Lang NP (2012) Quality of reporting of clinical studies to assess and compare performance of implant-supported restorations. J Clin Periodontol 39: 139-59. [Crossref]
21. Hammerle CH, Stone P, Jung RE, Kapos T, Brodala N (2009) Consensus statements and recommended clinical procedures regarding computer-assisted implant dentistry. Int J Oral Maxillofac Implants 24: 126-131. [Crossref]
22. Harder S, Kern M (2009) Survival and complications of computer aided-designing and computer-aided manufacturing vs. conventionally fabricated implant-supported reconstructions: a systematic review. Clin Oral Implant Res 20: 48-54. [Crossref]
23. Kapos T, Ashy LM, Gallucci GO, Weber HP, Wismeijer D (2009) Computer-aided design and computer-assisted manufacturing in prosthetic implant dentistry. Int J Oral Maxillofac Implants 24: 110-117.  [Crossref]
24. Lewis MB, Klineberg I (2011) Prosthodontic considerations designed to optimize outcomes for single-tooth implants. A review of the literature. Aust Dent J 56: 181-192. [Crossref]
25. Abduo J, Lyons K, Bennani V, Waddell N, Swain M (2011) Fit of screw-retained fixed implant frameworks fabricated by different methods: a systematic review. Int J Prosthod 24: 207-220. [Crossref]
26. Ramos BC, Albrektsson T, Wennerberg A (2014) Dental implants inserted in fresh extraction sockets versus healed sites: A systematic review and meta-analysis. J Dent 43: 16-41. [Crossref]
27. Schrott A, Riggi-Heiniger M, Maruo K, Gallucci G (2014) Implant loading protocols for partially edentulous patients with extended edentulous sites- a systematic review and meta-analysis. Int J Oral Maxillofac Implants 29: 239-255. [Crossref]
28. Pozzi A, Tallarico M, Moy PK (2014) Three-year post-loading results of a randomised, controlled, split-mouth trial comparing implants with different prosthetic interfaces and design in partially posterior edentulous mandibles. Eur J Oral Implantol 7: 47-61. [Crossref]
29. Lozada JL, Garbacea A, Goodacre CJ, Kattadiyil MT (2014) Use of a digitally planned and fabricated mandibular complete denture for easy conversion to an immediately loaded provisional fixed complete denture. part 1. planning and surgical phase. Int J Prosthodont 27: 417-421. [Crossref]
30. Delben JA, Goiato MC, Pellizzer EP, Filho OM (2012) Planning for Immediate loading of implant-supported prostheses: literature review. J Oral Implantol 38: 504-508. [Crossref]
31. Jokstad A, Carr AB (2007) What is the effect on outcomes of time-to-loading of a fixed or removable prosthesis placed on implant(s)? Int J Oral Maxillofac Implants 22: 19-48. [Crossref]
32. Grütter L, Belser UC (2009) Implant loading protocols for the partially edentulous esthetic zone. Int J Oral Maxillofac Implants 24: 169-179. [Crossref]
33. Esposito M, Grusovin MG, Coulthard P, Worthington HV (2008) The efficacy of interventions to treat peri-implantitis: a Cochrane systematic review of randomised controlled clinical trials. Eur J Oral Implantol 1: 111-125. [Crossref]
34. Gallucci GO, Morton D, Weber HP (2009) Loading protocols for dental implants in edentulous patients. Int J Oral Maxillofac Implants 24: 132-146. [Crossref]
35. Atieh MA, Atieh AH, Payne AG, Duncan WJ (2009) Immediate loading with single implant crowns: a systematic review and meta-analysis. Int J Prosthodont 22: 378-387. [Crossref]
36. Cordaro L, Torsello F, Roccuzzo M (2009) Implant loading protocols for the partially edentulous posterior mandible. Int J Oral Maxillofac Implants 24: 158-168. [Crossref]
37. Roccuzzo M, Wilson TG, Jr (2009) A prospective study of 3 weeks' loading of chemically modified titanium implants in the maxillary molar region: 1-year results. Int J Oral Maxillofac Implants 24: 65-72. [Crossref]
38. Lee CY, Hasegawa H (2008) Immediate load and esthetic zone considerations to replace maxillary incisor teeth using a new zirconia implant abutment in the bone grafted anterior maxilla. J Oral Implantol 34: 259-267. [Crossref]
39. Pita MS, Anchieta RB, Barão VA, Garcia IR Jr, Pedrazzi V, et al. (2011) Prosthetic platforms in implant dentistry. J Craniofac Surg 22: 2327-2331. [Crossref]
40. Verma R, Verma T, Bragger U, Wittneben G (2013) A systematic review of the clinical performance of tooth-Retained and implant-retained double crown prostheses with a follow-up of 3 years. J Prosthodont 22: 2-12. [Crossref]
41. Morton D, Chen ST, Martin WC, Levine RA, Buser D (2014) Consensus statements and recommended clinical procedures regarding optimizing esthetic outcomes in implant dentistry. Int J Oral Maxillofac Implants 29: 206-221. [Crossref]
42. Rodriguez AM, Rosenstiel SF (2012) Esthetic considerations related to bone and soft tissue maintenance and development around dental implants: report of the Committee on Research in Fixed Prosthodontics of the American Academy of Fixed Prosthodontics. J Prosthet Dent 108: 259-267. [Crossref]

Conflict of interest

The authors claim no conflicts of interests.