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Table of Contents
REVIEW ARTICLE
Year : 2019  |  Volume : 9  |  Issue : 2  |  Page : 66-76

Implant prosthodontics: Challenges, complications, and solutions


Private Practice, Mumbai, Maharashtra, India

Date of Web Publication13-Jan-2020

Correspondence Address:
Dr. Ali Tunkiwala
Ground Floor, Nirant Building, 19th Road, Khar West, Mumbai - 400 052, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdi.jdi_14_19

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   Abstract 

Contemporary implant dentistry needs to provide solutions to our patients that are not only functional but also esthetically correct and have the inbuilt strength and mechanisms to provide longevity without any major biologic or hardware complications. In case such complications occur, there must be a well laid out pathway for their management. This article discusses common hardware issues with implant dentistry and ways to prevent them and manage them.

Keywords: Breakage, hardware complications, implant dentistry, implant prosthodontics


How to cite this article:
Tunkiwala A, Kher U. Implant prosthodontics: Challenges, complications, and solutions. J Dent Implant 2019;9:66-76

How to cite this URL:
Tunkiwala A, Kher U. Implant prosthodontics: Challenges, complications, and solutions. J Dent Implant [serial online] 2019 [cited 2020 Jun 4];9:66-76. Available from: http://www.jdionline.org/text.asp?2019/9/2/66/275695


   Introduction Top


Implant dentistry has matured from the early days where the main goal was to provide function. Today, the need of the hour is to provide function with long-term esthetics that respects the parameters of hard- and soft-tissue biology and preserves the surrounding bone architecture around functional implants for decades. This puts a unique responsibility on the clinicians today, who need to train from the biologic perspective to place the implant in stable tissues and from a technical perspective to prevent long term prosthetic complications. Given the large number of implants placed in recent times, the complications experienced are only bound to increase. Moreover, if such complication does end up occurring, there has to be a pathway and protocol to manage these without extensive intervention and remakes.


   Classifying Complications Top


Complications in implants can be divided into:[1]

  1. Biological complications associated with preimplant tissues (mucosa and/or bone)
  2. Hardware complications associated with implant and/or prosthetic components.


This article aims to address the etiology and present clinical insights into some of the common hardware complications. It is by no means a comprehensive guide on the vast subject of complications around implants.

Biological complications

In this category of complications, it is necessary to differentiate between peri-implant mucositis (not involving peri-implant bone loss) and peri-implantitis (involving progressive peri-implant crestal bone loss). At the stage of mucositis, the disease can be considered reversible. Appropriate measures such as diligent oral hygiene, mechanical debridement with antiseptics and/or change in prosthetic contours need to be carried out to prevent further progress of the disease [Figure 1], [Figure 2], [Figure 3]. In [Figure 2] observe the proximity of the frenal attachment to the site of peri-implant inflammation and lack of attached mucosa. This could be attributed as a cause in conjunction with buccal malposition of the implants.
Figure 1: Clinical photo depicting peri-implant mucositis

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Figure 2: Clinical picture of peri-implantitis after 8 years in function. Suppuration is a sign of peri-implantitis

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Figure 3: Peri-implantitis manifests itself in the form of crestal bone loss

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It is incumbent upon the clinicians to consider factors that will allow a healthy biologic environment around the implant. These include sufficient keratinized mucosa and bone volume at the implant site, adequate distance between implants, correct three-dimensional (3D) implant positioning, and designing a prosthesis with adequate cleanability. Restorative solutions that allow hygiene measures such as overdentures may be preferred in some patients over fixed solutions. Hygiene assumes greater importance in designing of the prostheses [Figure 4].
Figure 4: Poor design of the prostheses makes hygiene difficult and leads to peri-implant infection

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Hardware complications

In this category of complications, it is necessary to differentiate between technical complications (that affects laboratory-fabricated components of the prostheses) and mechanical complications (those that are associated with manufacturer-fabricated components).

Hardware complications can manifest at various interfaces that hold implant components and prostheses together. It is necessary to understand these and analyze problems at different levels. When a force is produced on an implant prosthesis, it has to get transmitted through the structure of the prostheses and along the body of the implant to finally get dissipated in the bone. The bony trabeculae that house the implant perform the role of dissipation of stresses by creating a 3D network within the bony architecture. The prostheses will thus be only as strong as its weakest link. In certain cases, the weakest link may be the veneering material, whereas in others, it may be an abutment screw that holds it all together. The goal in implant prosthodontics is to design this weakest link to be strong and resilient enough to manage the forces of occlusion.

We analyze these hardware complications under the following headings:[1]

  1. Implant fracture
  2. Implant body-abutment interface
  3. Abutment screw
  4. Abutment body
  5. Interface between the abutment and the reconstruction
  6. Attachment systems for overdentures
  7. The prosthetic reconstruction.


Implant fracture

[Figure 5] shows an implant body that has fractured in function. Implants are generally made from Grade IV titanium. They vary in body design, thread geometry, neck features, platform, connections, length, and diameter. They could be tissue level or bone level. The implant body has to withstand axial as well as nonaxial forces. The physical properties of the implant material should assure a certain amount of flexibility and strength to resist permanent deformation.
Figure 5: Implant fracture after loading with prostheses

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The main cause of such a catastrophic failure is increased load dynamics on the implant. This can be attributed to two clauses: one, the implant itself is malpositioned, such that even normal occlusal force now becomes detrimental for it, and second, the force itself maybe too high and thus even a well-placed implant succumbs to the overload. Several factors will govern whether an implant can fracture in function. One of the key factors is the implant diameter. A narrow diameter implant used to replace a molar is prone to such mishaps [Figure 6].
Figure 6: Narrow diameter implants to replace large molars with long vertical cantilevers are at a risk of hardware complications such as implant fracture

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Anything that is 3.5 mm and lower is considered a narrow diameter. For molars, where the bite force is significantly higher, it is necessary to institute appropriate bone management techniques to place an implant of 4.5 mm and more in diameter. The length of the implant plays no role in this.

Chrcanovic et al.[2] concluded after their retrospective study that five factors had a statistically significant influence on the fracture of implants (increase/decrease in fracture probability): use of higher grades of titanium (decrease 72.9%), bruxism (increase 1819.5%), direct adjacency to cantilever (increase 247.6%), every 1 mm increase in implant length (increase 22.3%), and every 1-mm increase in implant diameter (decrease 96.9%). These findings can be directly extrapolated and applied to patient scenarios to have a robust plan to prevent implant fracture.

Another key factor to consider is the number of implants. Greater number of implants with appropriate regular or wide diameters are needed when the forces expected on the restorations are higher. In partially edentulous scenario, it is sometimes prudent to have one implant per missing tooth [Figure 7] and splint them together to allow better force dissipation in the system. Implant-supported bridges [Figure 8] must be done only when adequate diameter is achieved on the implant and that too in good quality bone. Whenever such bridges are constructed on an implant, it is prudent to restrict oneself to just one pontic in posterior areas. As the number of pontics increases, the flexion of the bridge increases by cube of its length and that will lead to detrimental forces on the supporting implants.
Figure 7: Three implants to support three missing teeth as the diameters are not large enough to have two implants and a pontic

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Figure 8: Two wide-diameter implants to support a three-unit bridge

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In most cases, a catastrophic fracture of the implant will need a change of prostheses. The offending implant will need to be removed using implant removal kits or a trephine to remove the surrounding bone with the implant. It is possible to place another implant in that region after a suitable healing period. If the treatment plan allows, such an implant may be cutoff and submerged and kept to rest (inactive) within the bone and a pontic constructed over it. Obviously, the patient needs to be informed of this treatment diversion.

Implant body-abutment interface

Implant abutment junctions have been a topic of discussion since implants came into vogue. The connections may be external, internal, conical, one-piece, two-piece, butt joint, or Morse taper. Geometrically, they may be hexagonal, octagonal, trilobular, and may have flat surfaces and notches in various permutations.[1] The length to which the abutment enters into the implant body is a factor to be discussed here as many designs exist that can engage the implant body just by a millimeter and others engage by as deep as 3 mm.

When an occlusal force is generated on the prostheses in function, there will be a micromovement between the implant and the abutment. This motion is said to be lesser with Morse taper connections and more with the butt joint connections.

This movement, if it occurs beyond the tolerance level of the material, can lead to abutment base fracture. A third-party abutment or one that has been fabricated as a clone of a better product without adequate testing may be prone to such a mishap. Needless to say, if the screw survives the onslaught of force, the abutment may be changed and prostheses redone. The use of well-documented and tested systems cannot be overemphasized here.

Misfit of abutment [Figure 9] into the implant can be a significant problem. This mainly happens due to faulty indexing of the abutment into the implants. Clinicians must verify the fit of components on a radiograph before the final delivery of the prostheses.
Figure 9: Misfits of abutments evident due to incorrect engagement with implant connection

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In recent times, there has been an increased use of base metal alloys to make custom abutments. When alloys such as cobalt-chromium are used to manufacture the connection of the abutment into the implant, caution has to be exercised as the harder alloy of the abutment may cause wear of the softer implant body. Reports of such wear and damage to internal surfaces of the implants have been well documented with the use of zirconia connections within the implants.[3]

One more aspect of implant-abutment interface that needs a mention is the ability of the junction to be sealed to prevent bacterial infection. A poor seal will lead to bacterial colonization of the junction that can be a nidus for infection and the resultant foul smell that emanates from the area when the junction is opened for maintenance purpose. It is important to use precision-fit components and torque the abutments to manufacturers' instructed values to avoid such problems.

Abutment screw

From a biomechanical standpoint, maintaining friction between the threads of the abutment screw and the bore of the implant remains a challenge even today. The mechanism of screw systems works by torquing the abutment screws to 25–35 Ncm. Torquing the screw will lead to elongation of the screw within its elastic limit. This will lead to a very intimate engagement between the screw and the implant body that will have the ability to withstand masticatory forces in the long term.

Two of the most common complications of abutment screws are screw loosening and screw fracture. Using original well-researched components of reputed systems will go a long way in avoiding this. Clinicians must exercise caution when an abutment or prosthetic screw has loosened. Any loosened screw must not be retorqued again. It is advisable to change the screw and use a new one. Retightening of a loose screw will lead to eventual breakage of the screw since, in the first instance of torquing, the screw was already stressed just below its elastic limit. When stressed again during retightening, the elastic limit may be crossed easily leading to permanent deformation (breakage). If screw loosening has occurred, the clinician must check the prostheses for misfits and also check occlusion to see that the implant prostheses are not overloaded, especially with nonaxial forces.

In case screw fracture has happened, the clinician must endeavor to retrieve the broken fragments to save the implant. The management of such mishaps depends on the level at which the screw has fractured. In most instances, it is the head of the screw that fractures from the shank [Figure 10] and [Figure 11].
Figure 10: Screw loosening followed by breakage at the junction between the head and shank

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Figure 11: The screw was retrieved carefully without damage to internal surface of the implant

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There are several screw retrieval kits that are available on the market. Most of them work by the principle of precision drilling the screw out and then retapping the internal surface of the implant to receive a larger diameter screw. This is easier said than done as the procedure is cumbersome and may not successfully work in all cases. Another method that may be explored is the use of ultrasonics to retrieve the broken fragment. This proves to be a valuable tool, but caution has to be exercised to prevent heat generation. The use of high-speed air rotors is contraindicated within the internal surface of the implant to retrieve the broken fragment as this will lead to damage of the internal surface to the implant. The use of high magnification in such cases cannot be overemphasized. Needless to say, if the screw cannot be retrieved by any means, the implant itself may need to be removed or buried and not used.

Another common complication of abutment screws is the damage to the head of the screw due to repeated use in the laboratory. This leads to an inability to torque the screw during delivery. The use of a laboratory screw should be made mandatory to avoid this problem. Most reputed implant manufacturers provide laboratory screws to be used in laboratory during making of the prostheses and its several trials. The clinician then delivers the final abutment screw that is fresh from the pack during installation of the prostheses. This protocol goes a long way in preventing screw loosening and breakage.

Abutment body

There are various materials with which abutments can be made today. Titanium and ceramic are the most commonly used materials, whereas resin-based materials such as polyether ether ketone and their variations are newer additions. Any abutment body may be prefabricated or customized. Any abutment chosen must have the physical integrity to survive long term, and if it fails, it should be easy to change to a new one without losing the implant. Thus, it is prudent to have a modular design that allows easy removal and replacement and have predetermined breaking points for uncomplicated removal of fractured components.

The superstructure can be screw retained or cement retained and will be discussed in detail in the next section.

The most common complication with the abutment body is the deformation or fracture of the abutment in function. Using the correct abutments for the desired indication and using well-reputed ones will be important to avoid this problem.

In case of customized zirconia or ceramic abutment that made by computer-aided design–computer-aided manufacturing fabrication methods, it is important to maintain sufficient thickness. If the abutment walls are thinned too much, it may lead to catastrophic fracture.

Another issue commonly faced is that the abutments used clinically sometimes have scratches or pits on them and accumulate a large amount of laboratory debris. It is important to examine abutments received from the laboratory under magnification and use enzymatic cleaners to remove debris. Autoclaving the abutments that have well-polished gingival collars will help in attachment of soft tissue, and the dictum of clean abutments must be imbibed in a responsible implant practice.

Interface between abutment and the reconstruction

This interface is decided by the choice of retention feature in the prostheses. The prostheses may be screw retained or cement retained. [Table 1] here summarizes the comparison points between the two options, adapted from www.iti.org.
Table 1: Screw retained vs cement retained restorations

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In a nutshell, the screw retained has retrievability, but passivity is difficult to achieve unless precision procedures are followed in laboratory and clinical work. Microbial colonization in the gap of screw-retained restorations with potentially pathologic bacteria has been proved (Keller et al. 1998). Cement retained are great for angulation correction, but residual cement in the sulcus is a potential disadvantage, but not something that cannot be easily overcome. A cement-retained restoration will need a minimum of 8-mm restorative space. Moreover, the same microbial colonization that happens in screw-retained restorations may happen in margins of the restorations if they have a misfit [Figure 12] and [Figure 13].
Figure 12: Cement-retained restoration for #46

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Figure 13: Screw-retained prostheses splinting multiple implants

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When we are discussing screw-retained and cemented restoration, the discussion would be incomplete if the surgical protocol for each is not touched upon.

For a single-tooth restoration, if the plan is to make a screw-retained restoration, surgical implant placement has to be perfect in all three dimensions. If the implant is too buccal or palatal [Figure 14] and [Figure 15], it will jeopardize the ability to have the screw access hole in the right position such as the cingulum of an anterior tooth or occlusal surface of a posterior tooth. The use of a surgical stent in these cases is mandatory.
Figure 14: Surgical stent guides the clinician in correct three-dimensional positioning of the implant

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Figure 15: The final restoration with palatal screw access allows for retrievability

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On the other hand, in multiple implant cases, there is a limited flexibility offered by screw-retained option in surgical implant placement mainly in the mesiodistal position. The implants may be placed conveniently as per bone availability and still that would not become a prosthetic complication as the teeth will be set on the framework according to esthetic and phonetic needs [Figure 16]. The placement of implants in cases where a cement-retained option is thought of is more exacting as we do not want the abutment to emerge in the proposed interdental areas of the final prostheses [Figure 17], thus making hygiene difficult.
Figure 16: Screw-retained full arch restorations allow for a limited leeway in mesiodistal positioning of the implant

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Figure 17: Cement-retained restorations require greater surgical precision to have the implants exactly where the proposed teeth axis will be

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Both these types of restorations can be fought for and against by their proponents and opponents. It would be a boon if the advantages of both can be combined in the same prostheses and disadvantages almost eliminated.

One such option in single units is to make a cement-retained restoration on prefabricated abutment and maintain the viability of the screw access hole [Figure 18]. In this design, a permanent cement must be used to lute the prostheses onto the abutment. The screw access acts as a vent to allow the escape of excess cement easily [Figure 19] and [Figure 20]. In the future, the restoration may be retrieved through the screw access. For this, the implant trajectory must emerge from occlusal of posteriors or cingulum of anterior. Another major advantage of this design is that an industrially manufactured machined component engages the implant connection, thereby reducing misfits at the crucial implant-abutment interface.
Figure 18: The cement-retained crown with screw access open to allow for easy retrievability while taking care of cement access

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Figure 19: The excess cement extrudes out of the occlusal vent with very little cement that can trickle into the sulcus

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Figure 20: The restoration is then unscrewed and any excess cement is cleaned up before torquing it back in

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Clinicians must understand that all screw-retained restorations are not created equal. There are many ways to make a screw-retained restoration. Three most common ways are:

  1. Using a full plastic burnout cylinder [Figure 21] so that the entire framework including the implant connection is casted. This is the worst way to do a screw-retained restoration as castings (with base metal alloys) are never accurate and passive to the same degree as industrial machining and that may result in a less than optimum engagement of the implant connection. This results in inappropriate transfer of stresses to the implant and more forces on the screws in function leading to screw loosening or breakage. Needless to say, a casting done in noble metal can be cut and soldered to achieve passivity but still engaging the implant component
  2. Using a UCLA (University of California & Los Angeles) abutment [Figure 22] in which the implant connection is machined and the plastic portion of the abutment is used to burnout in casting technique. This is a better way to make screw-retained frameworks as the part that fits in the implant is industry manufactured and precise. The only challenge that remains is achieving passivity of the framework. Alloys that can be soldered may be used here so that the passivity can be achieved by sectioning the framework and soldering when needed.
  3. With the advent of digital technology, a titanium base abutment can be used on which the superstructure can be milled and luted [Figure 23] and [Figure 24]. In this method, an industry manufactured part engages the implant. However, the retentive elements of several titanium base abutments on the markets are short in height and that can lead to dislodgement of the superstructure in function. The industry has to work toward avoiding this.
Figure 21: Plastic burnout cylinders are waxed up to desired shape and casted with base metal alloys. Not a good way to connect to the implant

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Figure 22: UCLA abutments have machined, industry manufactured component that engages the implant. The superstructure is casted to it

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Figure 23: A titanium base can be used to make a screw-retained restoration on which the superstructure can be milled and glued

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Figure 24: The final screw-retained restoration made on titanium base

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In [Figure 21], plastic burnout cylinders are waxed up to desired shape and casted mostly in base metal alloys to save cost. Since the implant connection is casted, it leads to a lot of inaccuracy as casting cannot reproduce the geometry accurately and consistently.

In conclusion, within the hierarchy of choice of prostheses type, it is important to remember that an industry manufactured machined component must always engage the implant to provide the best outcome.

The complications can be discussed as follows: with cement retained, the most common problems are loss of retention, screw loosening, and cement residue. Abutment height should be a minimum of 5 mm, and the abutment may be sandblasted for better retention. The cement residue can be taken care of by designing and selecting abutment collar heights such that the margins are no deeper than 1 mm. Radiographic control is important.

With screw-retained restorations, the most common complication is screw loosening or breakage and ceramic chipping. Following very precise clinical and laboratory procedures and checking for misfits with radiographs is crucial. Passivity can be confirmed with the Sheffield test. The management finally is the same as discussed in abutment screw section earlier in the article.

Attachment systems for overdentures

Implant overdentures can be of two types:

  1. Those that mainly derive retention from the implants
  2. Those that derive retention, stability, and support from the implants.


The former is known as implant-retained, tissue-supported overdenture [Figure 25] and requires a lesser number of implants. However, the denture cannot be flangeless or palate free as the tissue coverage provides crucial support. These types of overdentures may be splinted or unsplinted in the mandible with 2–4 implants. However, in the maxilla, splinting of implants used in overdenture treatment is important as the bone is softer and forces are not always along the long axis of the implants. A minimum of four implants are needed for the maxilla.
Figure 25: Implant-retained, tissue-supported denture needs good posterior ridge anatomy to be successful

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The latter is known as implant-supported overdenture [Figure 26] and requires more number of implants to engage the prostheses rigidly, thereby not allowing much movement of the prostheses. These types of overdentures are done in cases where the patient has sufficient bone, but a fixed restoration cannot be done due to hygiene or economic reasons. The prostheses may be with minimal flanges when needed adding to comfort.
Figure 26: With poor posterior ridge anatomy, it is required to place adequate number of implants to support and retain the denture. In the upper jaw, such dentures can be without a palatal coverage if needed

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Since a small retention area is responsible for the function of the full arch, overdentures of all types need considerable maintenance irrespective of the attachment system or the number of implants. The most common complications are wear of inserts and attachments leading to loosening of the denture. The worn parts need to be changed regularly, and their wear and tear depends on the force from the opposing arches as well as the support from the tissues. The clinician must endeavor to get the implants parallel to each other to optimize the retention derived from unsplinted implants. Hardware-related peri-implant mucositis and hyperplasia are not uncommon and may require the selection of appropriate collar heights to overcome the issue. Finally, breakage of the denture due to weakening and fatigue is important to overcome by making metal base dentures where possible.

The prosthetic reconstruction

The final teeth that are made for the patients will themselves undergo several complications. The prostheses have two main components that include the framework and the veneering material. [Figure 27] here summaries the material options.[4][Figure 28],[Figure 29],[Figure 30],[Figure 31].
Figure 27: Framework and veneering material options

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,
Figure 28: When the restorative space available for one arch is 10-12mm, Porcelain Fused to Metal or Zirconia is recommended

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,
Figure 29: When the restorative space available for one arch is 12-15mm, Porcelain Fused to Metal or Zirconia with pink ceramic or pink resin is recommended

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,
Figure 30: When the restorative space available for one arch is 15-18mm, milled titanium framework with individual ceramic crowns is recommended. Alternatively, Resin teeth with reinforced PEEK or a Metallic framework can be done too

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,
Figure 31: When the restorative space available for one arch is greater than 18mm, a fixed restoration is contrindicated. Implant Overdentures are needed here to provide lip support and hygiene

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.

Each of these has minimum restorative space requirements listed in [Table 2].
Table 2: Numerical guideline for selection of prostheses in full arch cases

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The most common problem encountered with the prosthetic reconstruction is the fracturing of the veneering material that could be a resin or ceramic. The second complication is the breakage of the framework material.

The occlusal adjustments of the prostheses should be such that there are uniform contacts of equal intensity on both sides and the chewing envelope of the patient needs to be respected. Acrylic resins have been frequently employed to make fixed reconstructions. Acrylic needs a space of 15 mm to 18 mm per arch, and the most common mistake is to choose this option for patients having insufficient interarch space [Figure 32]. If the space requirements of prostheses are respected, the connector dimensions on the framework will meet the minimum thickness needed and will not fracture during function.
Figure 32: Acrylic teeth are the wrong choice here as the space available is only 11 mm

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   Conclusion Top


Implant dentistry has now matured to a stage where there are set protocols for many treatment modalities that we have to offer our patients. The challenges that are presented by the unique conditions governed by patients' biologic and esthetic needs have to be overcome by plan for execution that will minimize biologic and hardware complications in implant dentistry. If these complications do occur, there should be enough leeway kept in the prostheses to manage that with the least functional and economic burden on the patient as well as on the practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Bragger U, Heitz-Mayfield LJA. Biological & Hardware Complications in Implant Dentistry. ITI Treatment Guide. Quintessence Publishing Co Ltd. Berlin 2015:8.  Back to cited text no. 1
    
2.
Chrcanovic BR, Kisch J, Albrektsson T, Wennerberg A. Factors influencing the fracture of dental implants. Clin Implant Dent Relat Res 2018;20:58-67.  Back to cited text no. 2
    
3.
Stimmelmayr M, Edelhoff D, Güth JF, Erdelt K, Happe A, Beuer F. Wear at the titanium-titanium and the titanium-zirconia implant-abutment interface: A comparative in vitro study. Dent Mater 2012;28:1215-20.  Back to cited text no. 3
    
4.
Tunkiwala A, Kher U, Bijlani P. Numerical guidelines for selection of implant supported prostheses for completely edentulous patient. Quintessence India 2017;1:46.  Back to cited text no. 4
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 13], [Figure 14], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30], [Figure 31], [Figure 12], [Figure 15], [Figure 25], [Figure 32]
 
 
    Tables

  [Table 1], [Table 2]



 

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