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Authors:Dr. Rathika Rai, Dr. Surojit Dutta, Dr. Ranjani Narayanamurthy

Abstract:

The success of Implant restoration is a multi-factorial and multi-step procedure . Right from the placing of implant to the final restoration,it needs a sensitive and sensible approach for the long term success of the implant restoration. Not only it demands a good hard tissue management, but also a delicate approach to the existing soft tissue around the implant. The component behind the formation of soft tissue cuff around implant reatoration is permucosal abutment .This articles describes about the various functions,parts and classification.
Key words: Permucosal abutment, gingival former, healing abutment ,classification of permucosal abutment.

Introduction:

Permucosal abutment otherwise also known as healing abutment , transmucosal attachment, healing cap ,gingival former ,protective cap and contour healers, an important component in the concept of non-submergible implant mode of concept to attain a healthy soft tissue cuff around the collar of implant for both anterior and posterior restoration . It can be defined as “any dental implant abutment used for a limited time to assist in healing or modification of the adjacent tissues.”(GPT-8)
Permucosal abutment of specific diameters and shapes are fixated on the implants to displace the gingiva from the space above the implant during the Implant healing time and serve for proper gingiva shaping(Fig 1 )
 
Fig 1. Permucosal abutment.
Functions of permucosalabutment :
  1. It helps in forming of soft tissue cuff around the implant. (Fig 2)
  2. Its helps to prevent the apical migration of theperi implant soft tissue
  3. Its forms a soft tissue barrier around the implant.(Fig 3)
  4. Encode permucosal abutments are used for digital impression .(Fig 4)
  5. It helps in establishing a esthetic profile in soft tissue level at anterior restoration.
  6. The recent permucosal abutment can be used as an alternative for impression coping at implant level impression.
  7. It has proved to be effective in platform switching concept for the bone formation
 
Fig 2. Formation of soft tissue cuff around implants



 
Fig 3. A close junction is formed around implant by the soft tissue.
Classification of permucosal abutment:

It can be classified based on the height, shape , material, surface, diameter and fabrication
  1. Based on height it can be classified as

  2. i) Short : less than 3mm.
    ii) Medium : 3-5mm
    iii) Long : more than 5 mm

  3. Based on shape it can be classified as :

  4. i) cylindrical,
    ii) wide body
    iii) bottleneck
    iv) conical
     
    Fig.4. Digital model with permucosal abutment.
  5. Based on material

  6. i) Titanium based
    ii) Non titanium based -PMMA, zirconia, PEEK AND PAEK.
  7. Based on fabrication :

  8. i) Prefabricated
    ii) Custom made.
    iii) CAD/CAM made.
  9. Based on surface it can be classified as :

  10. i) Polished or machined surface
    ii) Unpolished or etched surface.
    iii) Laset-Lok microgrooves
    Fig.5. Difference between connective tissue attachment around tooth and implant.




  11.  
  12.  
  13. Based on diameter :

  14. i) Thin : less than 4mm
    ii) Medium : 4-6 mm
    iii) Thick : more than 6 mm




Understanding mucosal barrier around implant and role of permucosal abutment:

To understand and appreciate the role of healing abutment, it is necessary to understand the gingival mucosal around implant.
 
Fig.6. Laser –lok in the shoulder of the permucosal abutment shown in the form of grey band. Fig.7. Parts of Permucosal abutment
 
Fig. 8. Identification markers in healing abutment.
A) The mucosal barrier around implant:

Tissue integration with dental implants is a normal wound healing process which involves several stages of tissue formation and degradation. The result of the modeling and remodeling phases that occur in the bone tissue is osseointegration, while the establishment of the mucosal barrier around the implant is characterized by a gradual shift from a coagulum to granulation tissue, followed by the formation of a barrier epithelium and the maturation of the connective tissue.

It consists of a barrier epithelium (2 mm long, on average) and 1 to 1.5 mm of “connective tissue integration.” Collagen fibers occur in large proportion..Peri implant tissues have similar characteristics to dentogingival tissues and are made up of epithelium and connective tissue.1,2. The dimensions and the components of peri-implant soft tissues around implants are similar to natural teeth, except for the shape that the connective tissue adopts in relation to the implant surface3-6.

In natural dentition, collagen fibers of the periodontal ligament are arranged radially and inserted into the cement of the tooth’s cervical area, which maximizes resistance to tension forces. While longitudinal and circumferential fibers whose axes are parallel or oblique establish themselves in the cervical area of titanium implants but without direct insertion of the connective tissue into the implant surface.


B) Role of surface modification in altering the mucosal barrier:

Soft tissue play a vital role in the maintaining the integrity of the implant. In the crestal area level , they prevent bacterial invasion by different mechanisms in each of their components, provide resistance to frictional forces arising during mastication, and limit the penetration of foreign bodies7-9.
In the article of Schupbach and Glauser10 they described four defense zones – sulcular epithelium, junctional epithelium, lamina propria, and gingival tissue fibers – with their specific function; the authors also mentioned that an orientation of the fibers perpendicular to the surface of the implant will hinder the apical migration of junctional epithelium.But still there exists a controversies regarding the arrangements of connective tissue fiber close to implant surface. It has been shown that microscopic irregularities, like those generated by acid etching, or porous surfaces could promote the presence of perpendicular fibers..
Another factor that can affect fiber orientation is the presence of keratinized tissue, which favors parallel fibers. Recently, other factors that might favor the presence of perpendicular fibers have been detected, such as microgrooves of 8 to 12 μm, which permit adherence and fibroblast growth and the direct adherence of collagen fibers in the treated area.11-13Likewise, the presence of an area of pits of 70 ±5 μm diameter has also been successfully seen to favor fibroblast adherence and perpendicular connective fibers in a dog model.
For titanium implants placed crestally without significant bone loss, the establishment of biologic width can be observed in the transmucosal zone of implants or in the healing or prosthetic abutments..This is the main reason ,why a gingival former is placed after the implant surgery to establish a soft tissue cuff around the implant prosthesis specially in the anterior region for an acceptable esthetics .Not only this ,gingival former provides an seal between the prosthetic part and the external environment by forming a tight connection around the implant. ).
Commonly observed crestal bone resorption, or “dieback,” to the first coronally positioned implant thread following abutment attachment threatens the needed balance between the stable underlying bone and overlying soft tissues. Multiple causes of such undesirable crestal bone resorption have been investigated, including the inherent need for a minimum biologic width dimension, as seen in the natural dentition, and the bacterial and inflammatory cell infiltrate present at the Implant-abutment junction micro gap.
This inflammatory cell–laden connective tissue adjacent to the Implant abutment junction micro gap forces the repositioning of non-inflamed peri-implant connective tissue and the crestal bone apically. The relatively constant spatial relationship between the implant abutment junction and the alveolar crest confirms the approximate 1.5- to 2-mm apical position of the bony crest relative to the implant abutment interface.
With constant research and investigation surface modification like Laser-ablated microgrooved implant surface depths and widths in the range of 8 to 12 μm appear to regulate epithelial, fibroblastic, and osteoblastic cellular migration and orientation across these topographically altered surfaces around the collar of implants.. A recent prospective proof-of-principle human study demonstrated that these configured 8- and 12-μm microgrooves placed on the collar of dental implants allowed direct supracrestal connective tissue attachment to the implant collar.
This finding drew the idea of incorporating such features to the regular machine healing abutment for a better soft tissue connection around it.(Fig 6 )Myron Nevins(14)and his colleagues did a study on the connective tissue attachment to laser micro grooved abutments and confirmed the cellular soft tissue activity at the peri-abutment soft tissue interface and prevent commonly seen micro gap in between implant abutment junction by forming direct connective tissue attachment .
 
Fig.9. Adequate required height of permucosal abutment.
Gerhard Iglhaut et.al 15 did a study on the impact of disconnection and reconnection of the laser micro grooved and machined implant abutments on soft and hard tissue healing in canine model and found that completely micro grooved abutments enhanced sub epithelial connective tissue attachment and preserved crestal bone level. Moreover he found that repeated reconnection and removal of the healing abutment causes significant soft and hard tissue changes in the canine model. For this reason, modifications have recently been made to the abutment surface with the aim of attempting to achieve the insertion of connective tissue and avoid the apical migration of junctional epithelium 16-19.
Marco Degiedi 20 tried to find the histological and immunohistochemical status of the peri implant soft tissue around machined and acid etched titanium healing abutment in a prospective randomized study .According to this study inflammatory infiltrate was mostly present in acid etched specimens. Their extension was much larger than that of the machined surfaced samples. Along with it a higher number of T and B lymphocytes were observed in etched specimens. Higher values of micro vessel density and a higher expression of vascular endothelial growth factor intensity were also observed.
Not only was this, the Ki-67, NOS1 and NOS3 expression significantly higher in the etched specimens. All these results showed that the tissues around etched healing caps underwent a higher rate of restorative processes, most probably correlated to the higher inflammation processes observed in these tissues. It might be interesting to know for a prosthodontist to the difference between a implant restorative case with and without gingival former.
In a study done by E mumchu,Hbihan and O geckili21 on the influence of healing type on the marginal bone levels of implant supporting mandibular overdenture ,revealed that the marginal bone loss of the implant at 6 month was found to be significantly in submerged healing group.In another two study done by DietmarWeng et al 22,23 on the influence of micro gap location and configuration on radiographic bone loss around submerged and non-submerged implants ( done separately ),the bone loss was significantly less around non submerged implants than on submerged implants .
 
Fig 10. Landmarks used for the histometrical measurements. PM, periimplant mucosal margin; aBE, apical endoofthe barrier epithelium; S, multibase abutment shoulder; BIC, first bone-to-implant contact; BC, bone crest. Under calcifiedground B-L section, surface stained with LevaiLaczk_o – 1 mm magnification).
Parts of permucosal abutment:

A gingival former consist of a roof and a occlusally applicable screw. The  roof part having a top surface, an outer circumferential surface, a lower circumferential shoulder edge, and a conical mating shoulder with a bevel of 45 degree located on an underside of roof part of a shape complementary to a shoulder of the implant.(Fig 7) The top of the roof is a dome shaped and consists of a hex shaped hole for the drive to go in and at least two information marker regarding the dimension of the healing abutment thereby helping the dentist to identify the dimension.

The outer circumferential surface or the gingiva attaching side are usually cylindrical in shape and consist of information markers .Specifically, the information markers, when used in combination, permit identification of the healing abutment height, healing abutment diameter, dimensions of the attached implant seating surface, and implant hex orientation. It is further contemplated that the top or side surface of the healing abutment can be etched or defined with a polygonal, numerical, or line marking to indicate height, location and orientation of the underlying hex, abutment and/or implant.

Machined notches are one example of information markers. The quantity of notches and the location on the top and/or side surface of the healing implant can identify, for example, the height and diameter of the healing abutment.(Fig 8) A numeral may also appear on the top or side surface of the healing implant as an information marker. For example, a “4” might indicate a 4 mm tall healing abutment or a 4 mm diameter healing abutment.

A barcode can also be disposed on the top or side surface of the healing abutment of the present invention. This barcode is pre-coded with most of the dimensional variables of a particular healing abutment. The laboratory or dentist would only then have to use a barcode reader and display to obtain all of the required information about the healing abutment. A dentist utilizes a barcode reader to obtain this information, it would only be necessary to identify the angular orientation of the implant hex by information markers on the top or side surface of the healing abutment.

The top and/or side surface of the healing abutment could also contain recessed dimples or raised pimples as information markers.  The different types of information markers can be used, either alone or in combination, to help the dentist and the laboratory determine the different variables of the healing abutment and the implant.

Selection of permucosal abutment :

The permucosal abutment and final abutment should be selected so that they correspond in prosthetic range and gingival height. The description of the height of the gingiva former refers to the region from the interface level to the edge of the crown. It is always approximately 1.5 mm higher than the nominal height, viewed from the interface level .(Fig. 9)

Impression procedures and its effect on soft and hard peri-implant tissues:

As mentioned above, the structure of soft tissue around implants which is mostly collagen fibers and are delicate. Any disturbance to their arrangement may cause negative effect both on soft tissue and hard tissue around it.in studies over animals showed that a five times removal and fixing of healing abutment caused apical migration of the soft tissue around the implant.
To proceed with the restorative phase both in single or two stage implant surgery, subsequent removal and fixing of healing abutment becomes an mandatory step .this frequent removal and fixing causes some changes for the formed soft tissue cuff around the implant. But does this changes effect the life of an implant restoration? The answer to this is controversial and needs further investigation but a short term randomized controlled clinical trial was conducted by Theofilos et al on the effect of healing abutment reconnection and disconnection on soft and hard peri-implant tissues, showed no changes in reconnection and disconnection of healing abutment for two times.

Link between permucosal abutment and platform switching concept:

Lazzara and Porter (2006) (24) were the first one to define this biomechanical concept under the name of “platform switching”. According to his study, when the outer edge of the implant–abutment interface is horizontally repositioned inwardly and away from the outer edge of the implant platform, the crestal bone remodeling is altered vertically. This was evident on radiographs at mesial and distal sites of osseointegrated implants.
The biologic rationale for the platform switching concept as suggested by the author is that deliberate mismatching of the implant platform and abutment diameter repositions the inflammatory cell infiltrate zone surrounding the abutment further away from crestal bone and relocates the inflammatory infiltrate within an approximately ≤90- degree confined area of exposure, instead of a ≤180-degree area of direct exposure to the surrounding hard and soft tissues. On the other hand, several animal (Becker et al. 2007; Becker et al.
2009) (26,27) and human studies (Nentwig 2004; Enkling et al. 2011)(28,29) have failed to find a significant difference in bone remodeling between platform and non–platform switching implants. Finally, one recent systematic review found a beneficial effect of platform switching implants on peri-implant marginal bone (Al-Nsour et al. 2012)(30). Few studies has used this concept on the healing abutments.
One of them is done by Gary Finelleon peri implant soft tissue adaptation with non-matching healing abutments(Fig 10 ) .The study found that with a narrow healing cap showed an interproximal mesial bone up to 1mm above the implant shoulder where wider one showed a mean of .5 mm. However, this type of horizontal offset causes very minimal amount of bony changes at implant level.
Fig 10.Landmarks used for the histometrical measurements. PM, peri-implant mucosal margin; aBE, apical endo ofthe barrier epithelium; S, multibase abutment shoulder; BIC, first bone-to-implant contact; BC, bone crest. Under calcified ground B-L section, surface stained with LevaiLaczk_o – 1 mm magnification).

Bioflim around permucosal abutment:

The formation of biological film is an unavoidable situation in an oral cavity. But for successful long-term prosthetic rehabilitation, it is necessary to inhibit bacterial biofilm formation on implant surfaces, as these bacterial communities are the main sources of inflammation of the peri-implant mucosa and bone. Untreated peri-implantitis may lead to the even loss of dental implants. The first step for oral biofilm development consists in the formation of a salivary pellicle on all oral surfaces.
This coating contains host proteins and glycoproteins which serve as adhesion molecules for several species of bacteria. Streptococci (Streptococcus oralis,Streptococcus mitis) make up a high percentage of these first colonizers. These bacteria provide adhesion source for further bacterial genera, such as Actinomycesor Fusobacterium. In this second phase of biofilm development, the cellular concentration of chemical signals secreted by the colonizing bacteria reaches a critical point at which the cells start to synthesize and express exopolysaccharides (EPS).
These macromolecules make up the biofilm matrix, incorporating the bacteria. This matrix provide a high tolerance level against the shear forces of the oral fluids and the movement of tongue and jaw , making it almost impossible to detach from the surface. In a Study conducted by DomenicoBaldi et al , plaque accumulation was found more again in dual etched healing abutment as compared to the machined but no significant bleeding on probing on both the groups.31

Sebastin ,weiland,juergen and meile conducted a study on structural analysis of in situ biofilm formation on oral titanium implants and found that the thickness of biofilm vary from patient to patient with a range of 0 to 80 µm and a surface coverage up to 97% of the abutment surfaces. Also, biofilm was found thicker in the mandibular section than on maxillary.32

One of the disadvantages might be possibility of malodor. Malodor is often caused by microbes specially bacteria. Bacteria breakdown the oral protein into amino acid and further these amino acid into malodorous compounds like hydrogen sulfide and methymercaptan. Various studies have demonstrated the micro leakage occupying the internal compartment of the implant-abutment interface of 2 stage dental implant system.
it is hardly surprising that the opening of a healing abutment is often accompanied by malodor showing possible presence of harmful bacterial. Nirsterer along with Tamary,Mira and Ervin did a study on the link between transmucosal depth of osseointegrated implants and malodor production on 14 patients with 59 two stage implant surgery and found that with the increase of the transmucosal depth ,there is a increased malodor related parameters.33

Summary:

Permucosal abutment is basically made up of titanium grade 4 which make it extremely biocompatible. Its shape and form is designed for various situation but with a common motive forming a healthy soft tissue cuff around the final restoration. This cuff in the anterior region helps to attain expectable esthetics in implant dentistry.
Various studies and investigations have been done on its surface modification and its role to the peri implant tissue. Histological findings revealed a intimate contact of collagen fibers around the implant.

Conclusion :

Permucosal abutment as known with its many names not only protects the soft tissue but also enhances the life of implant restoration. Its role in forming a tight connection between the soft tissue and the prosthesis by forming a soft tissue cuff is really appreciable after the removal of permucosal abutment.
This acts as a barrier between the implant and outer environment. The intimate connection between the soft tissue and the implant can be enhanced with surface modification like etching or laser-lok method. These enhanced connections may improve the life of the restored implant dentition and a healthy gingiva around the restoration.

References
 
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