5.3.3 Technical Factors
5.3.3.1 Implant Positioning Errors
Implant fixture position has a direct impact on many aspects of the future outcome of the implant supported restoration, and subsequently peri‐implant tissue viola- tion. For instance, placing the implants too far labially will also lead to resorption of the thin labial plate followed by apical displacement of labial tissue complex, as shown in Figure 5.20a and b.
Implant fixture position has a direct impact on many aspects of the future outcome of the implant supported restoration, and subsequently peri‐implant tissue viola- tion. For instance, placing the implants too far labially will also lead to resorption of the thin labial plate followed by apical displacement of labial tissue complex, as shown in Figure 5.20a and b.
The extent of resorption appears more pronounced when the implant shoulder is placed less than half a millimeter from the crestal plate buccolingually (Ramanauskaite and Juodzbalys 2016).
Incorrect implant position in the alveolar ridge may occur because of many factors, such as not using a surgical guide, imprecise fabrication of a surgical guide, lack of control during the drilling procedure, poor pre‐ surgical planning, poor armamentarium, incomplete knowledge, and in experience. A minor deviation from the standard known clinical guidelines for esthetic implant positioning in any dimension will surely result in esthetic fallout, as shown in Figure 5.21a and b.
To establish and maintain an ideal soft tissue archi- tecture, implants should be positioned at the correct distance to the adjacent dentition, at the correct depth, and more palatally positioned (Choquet et al. 2001; Grunder et al. 2005; Kan et al. 2003). When dealing with anterior single implant supported restorations, the thickness of facial bone as well as the dimensions of the facial peri‐implant mucosa are critical for the achieve- ment and long‐term stability of good esthetics, with a reduced risk of future tissue recession (Buser et al. 2004; Grunder et al. 2005). When implants are incorrectly angled or improperly positioned, various prosthodontic techniques have been reported, includ- ing the use of a gingiva‐colored acrylic resin façade, a flexible silicone‐based tissue‐colored material, or removable prostheses (Cura, Saraҫoglu and Cötert 2002; Everhart and Cavazos 1983; Gardner and Stankewitz 1982; Greene 1998).
Juodzbalyus and Wang (2007) stated that a natural buccal and proximal restorative contour can be ensured by correctly orienting the implant in a buccopalatal position. A minimum space of 2 mm should be main- tained on the buccal side in front of the external implant collar surface, and correct three‐dimensional implant positioning has been considered important for long term maintenance of soft tissue levels (Buser et al. 2004). An association of buccal implant malpositioning and mid‐facial recession has been described (Chen et al. 2007, 2009) and should be considered by sur- geons when pursuing immediate implant placement. Studies identified the tooth‐to‐implant distance and the level of the contact point in relation to the bone crest as key factors for maintaining healthy papillae (Lops et al. 2008; Romeo et al. 2008).
It is essential that the clinician is familiar with the various unfortunate clinical situations that may arise due to misplacement and the ways to solve them. The axial misplacement of the dental implant within its hosing can be damaging to the overall health of the soft and hard tissues surrounding the implant, as a resulting deep gingival sulcus with a long junctional epithelium can be a serious consequence due to the fur- ther deep positioning of the implant and the failure of hygiene practice. This creates a favorable environment for several types of bacteria, including anaerobic bacte- ria, to colonize and populate. The deeper an implant is inserted into the bone, the more bone will be resorbed around the implant following second‐stage surgery with an abutment connection. This bone resorption is not a pathological condition but a physiological reac- tion to the implant misplacement. Inflammation and gingival bleeding usually occur as a result of the inac- cessibility for hygiene measures from one side and bac- terial endotoxins from another side. It becomes increasingly urgent to ensure complete removal of the excess luting cement from the interface between the abutment and the restoration. Correction of this clini- cal dilemma is almost impossible to achieve unless supragingival margins of the prosthesis are fabricated.
The failure to position the implant at its optimal depth, such as being placed too shallow, often results in a short crown with constricted margins due to the absence of the “running room.” This makes stacking the prosthetic components supragingival. This clinical predicament is impossible to amend or rectify. The difficulty remains in handling the margins of the final prosthesis and hiding the abutment collar sublingually. In this particular condi- tion, implant removal can be the treatment of choice. The improper mesiodistal positioning of the implant might lead to the total absence of restorative possibilities, and if the implant is placed in the interdental papilla space or is placed too mesialized or leaving no or a minimal space for restoration, it becomes impossible to restore. Violating the labial plate of bone or the labial soft tissues might constitute a major clinical dilemma that is impossible to correct even with the use of the angulated abutments. The consequences of violating the labial plate integrity goes beyond the teeth to the lip support, as it might impinge on lip harmony. Placing the implant angulation in a too‐far lingual position might result in tongue crowd- ing, because to impinge on the tongue space can significantly compromise speech and mastication.
A fair number of clinical approaches have been described to resolve misaligned and malpositioned dental implants if an unfavorable inclination of the implant fixture is the only problem. The use of angu- lated abutments can often improve the prosthetic results of an implant‐supported restoration. Even using the preangulated abutments in too‐far labial implant placement cases will not be effective in most clinical situations because the preangled abutment usually requires a larger restorative dimension than other types and the gingival collar of the preangled abutment will encroach upon the peri‐implant soft tissue and violate its natural contours. The use of the angled abutments will not ensure any protection against recession.
Several factors have been proposed as being important in determining the stability of the peri‐implant marginal mucosa, including the implant shoulder position in a buccolingual and apicocoronal plane (Buser et al. 2004; Garber 1981). In relation to the optimal buccolingual position, Buser et al. (2004) recommended that the implant shoulder should be placed 1–2 mm lingual to the emergence of the adjacent teeth to ensure maintenance of an adequate width of buccal bone and stable mucosa over the buccal implant surface. Evans and Chen (2008) suggested that the buccolingual position of the implant shoulder is a highly significant factor in determining the degree of buccal marginal tissue recession. Implants with a shoulder position at or buccal to a line drawn between the cervical margins of adjacent teeth demonstrated three times more recession than implants with a shoul- der position lingual to this line.
5.3.3.2 The Influence of the Implant Collar Design
The peri‐implant crest module is the collar portion of the dental implant creating a transition zone between the prosthetic part and the implant body. Its design and position in relation to the alveolar crest is critical and its relationship to the abutment implant interface plays a major role in overall harmonious integration and soft tis- sue health. Early tissue breakdown leading to soft tissue and hard tissue loss starts at the crest module. Misch, Qu and Bidez (1999) have studied the influence of the implant crest components and their angulation in relation to the shear and compressive loading. Smooth surface implant collars have been extensively used in past decades; however, a significant drawback of the smooth collar stems from its questionable integration with the surrounding hard tissues. When the smooth collar of an implant is placed under the crest of the bone, increased shear forces are created to the adjacent bone, and eventually bone is resorbed, leading to a marginal bone loss with a long junctional epithelium (Hermann et al. 2001). Hermann et al. (2001) examined the peri‐ implant soft tissue dimensions at varying locations of a rough/smooth implant border in one‐piece and two‐ piece implants in relation to the crest of the bone, when submerged and non‐submerged techniques were employed. Crestal bone changes around two types of implants with varying smooth collar lengths (2.8 and 1.8 mm) were evaluated. Their findings suggest an absence of bone loss was observed when the implants with rough crest modules were placed at the level of crestal bone, exhibiting a shorter (1.8 mm) as opposed to a slightly larger (2.8 mm) machined collar portion.
Weiner, Somin and Ehrenberg (2008) observed that initially the experimental implants showed greater bone attachment along the laser microtextured collar. However, the controls had more soft tissue downgrowth, greater osteoclastic activity, and increased saucerization compared with sites adjacent to experimental implants. There was closer adaptation of the bone to the laser microtextured collars. It was concluded that the use of tissue engineered collars with micro-grooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width (see page 158) (Nevins et al. 2008).
In a clinical study evaluating laser micro-texturing for soft tissue and bone attachments to dental implants, Pecora et al. (2009) incorporated a tapered dental implant (Laser‐Lok surface treatment) with a 2 mm wide collar, to accomplish bone and connective tissue attachment while inhibiting epithelial downgrowth in a prospective, controlled, multicenter clinical trial. A consistent differ- ence in the probing depth between Laser‐Lok and the control implant demonstrated the formation of a stable soft tissue seal above the crestal bone. Laser etched col- lars limited the crestal bone loss to the 0.59 mm range as opposed to the 1.94 mm crestal bone loss reported for the control implant (Elaskary 2009; Pecora et al. 2009; Ricci and Alexander 2001) (see Figure 5.22a and b).
A study of the effect of a machined/rough implant collar on the osseous crest has shown that the least marginal bone loss with each implant occurred when the collar of the implant was placed above the alveolar crest (Alomrami et al. 2005). A change in implant design towards a scal- loped collar to mirror the bone and soft tissue topography with rough surfaces and grooves did not prove to be practical (Wöhrle 2003). Also, it did not show any clinical benefits and made implant position orientation difficult. The last thread location of the implant determines the effective level of remodeling after loading, and this is per- haps even more important than the position of the implant/abutment microgap (Rompen, Touati and Van Dooren 2003). It is the author’s opinion that implants with microthreads reaching the collar do not seem to prevent bone resorption from occurring (see Figure 5.23a and b).
5.3.3.3 The Influence of the Provisional and Prosthetic Designs
The role of interim dental restorations used for optimizing the final result of the restorative and prosthodontic procedures has changed dramatically in the past few years. These restorations are no longer regarded as tem- porary restorations but rather as provisional restorations with distinct functions and purposes. Provisional resto- rations have become a vital diagnostic and assessment tool to evaluate function color, shape, contour, occlusion, periodontal response, implant healing, and overall esthetics. With increased demands placed on provisional restorations, new materials and techniques are being developed and some existing protocols are being refined to accomplish the desired goals. Provisional restorations are often in the oral environment for several weeks, requiring a precise fabrication. An adequate understand- ing of the relationship between periodontal tissues and restorative dentistry is paramount to ensure adequate form, function, and esthetics, as well as comfort of the dentition (Nugala, Kumar and Krishna 2012).
With dental implants, the clinical scenario is signifi- cantly different from that of a natural dentition, with the implant and/or abutment surface being a non‐vital struc- ture without a blood supply. Dental implant design and surface improvements have helped clinicians direct their treatment approach towards a more immediate timeta- ble as well as a more esthetically driven one (Smeets, Stadlinger and Schwarz 2016).
Many factors play a role in the emergence profile: (1) the smoothness and degree of finish of the temporization, (2) venting of the temporization to avoid excessive cement in the gingival crevice, (3) continuous changing of the pros- thetic margins in accordance with soft tissue maturation to provide steady soft tissue support, and (4) the cleanness and purity of the provisional materials. Using the provisional restoration for a sufficient time (four to six weeks) allows the soft tissue to reach its final healing stage and optimal maturation. Then when final prostheses are inserted, mini- mal or no tissue remodeling or migration occurrs.
The prosthetic stage is highly influential in the mainte- nance of peri‐implant tissue stability. It involves, the use of accurate provisional restorations, optimal final prosthetic fabrication, and a precise duration of the provisional resto- ration, which are all factors that need full attention. Implant provisional restorations provide significant and invaluable benefits such as enhanced patient comfort and satisfaction, as well as the ability to contour peri‐implant tissues (Botticelli et al. 2004). This is critical in the esthetic zone, where the contouring of the soft tissues provide an ideal emergence profile to aid in both esthetics and phonetics (Neale and Chee 1994; Chu et al. 2012; Hui et al. 2001).
The interfaces between the gingival unite and the implant collar is mainly composed of the epithelium and connective tissue, which forms the biological width (Abrahamsson et al. 1997; Berglundh et al. 1991; Hermann et al. 2000). The tissue at the most coronal aspect and adja- cent to the implant abutment consists of the free gingival margin, which is covered by stratified squamous epithe- lium. As the epithelium progresses down the implant it becomes non‐keratinized, below the junctional epithe- lium attachment lies the connective tissue attachment (McKinney et al. 1985). Current attention is driven towards the influence of the provisional restorations to the overall stability of the gingival tissues, and the optimal requirements of the provisional subgingival margins were described by (Luchinskaya et al. 2017).
Long‐term use of a provisional restoration should precede the insertion of the final prosthesis. This will help the matu- ration of the soft tissue during the provisionalization stage (Lazzara 1993), thus minimizing the tendency for future exposure of the final implant‐supported components. Especially in the esthetic zone, placing the provisional res- toration for a period of four to six weeks will provide the clinicians with the final mature gingival margin level after soft tissue remodeling has been finalized. In addition, long‐ term temporization will help to guide the soft tissues to mature and remodel, preventing eventual collapse. The rush for premature delivery of a prosthesis will lead to recession of the gingival tissue as the peri‐implant soft tis- sue continues to remodel (see Figure 5.24a and b).
In order to allow stable soft and hard tissue margins around the dental implant abutment, the transmucosal area of the abutment design should not be oversized and expanded but rather stay narrow and concave to thicken and immobilize the circular connective tissue around the connection. This induces thickening of the connective tissue zone, which will ensure long‐term stability of the marginal tissues (Touati, Rompen and Van Dooren 2005) (see Figure 5.25a and b).
The material composition of the implant transmucosal area, surface topography, surface tension, and surface energy have been studied over the years. Gittens et al. (2013) inves- tigated the influence of surface hydrophilicity of titanium implant surfaces on the behavior and differentiation of the epithelial cells. Spriano et al. (2017) suggested that surface hydrophilicity might positively influence the epithelial seal around dental implants. Proliferation, spreading, and mov- ing of the epithelial cells were enhanced on hydrophilic tita- nium surfaces compared with hydrophobic titanium surfaces. In addition, relatively smoother surfaces were pre- ferred (Novaes et al. 2010). Few articles have been found in the literature regarding cell adhesion or cell proliferation on to permanent abutment materials such as titanium, gold alloy, and ceramics (Abdulmajeed and Willberg 2015; Gasik 2016, 2017); however, we are expecting a huge leap in this path to develop in the near future that will help increase peri‐implant tissue stability around dental implant prosthet- ics. The prosthetic margins should be designed to avoid inducing too much pressure to the overlying soft tissues, as any extra pressure induced to the transmucosal area will be translated into apical migration of this tissue, especially in a thin tissue phenotype. The more pressure that is induced, the more liability there is for recession. Labial prosthetic margins should be either equi‐gingival slightly below gingival margin and the abutment shoulder should also be brought up to this level to allow the prosthetic margins to rest on it, leaving the transmucosal area intact and undis- turbed (Neale and Chee 1994) (see Figure 5.26).
5.3.3.4 Miscellaneous Factors
In natural dentition, gingival morphology is partly related to the tooth shape and form (Dhir 2011). Tooth crown morphology can be triangular, ovoid, or square shaped with a long, narrow, or short form. Olson and Lindhe (1991) in their study reported that individuals with a long narrow tooth form demonstrated a thin free gingiva, shallow probing depth, and pronounced scal- loped contour of the gingival margin. Similarly, the tooth shape and form can influence the peri‐implant soft tissue architecture. Tooth shape is one of the five essential diagnostic key factors for peri‐implant esthetics (Garber, Salama and Salama 2001; Kois and Kan 2001). These key factors include the relative tooth position, form of the periodontium, phenotype of the periodontium, tooth shape, and position of the osseous crest. According to Garber et al. (2001), subjects with a long narrow form of the upper central incisors experienced more recession of the gingival margin at buccal surfaces than subjects who had a short wide tooth form. Individuals with square‐ shaped teeth have more favorable esthetic outcomes because of the long proximal contact and less papillary tissue, whereas the triangular tooth shape has a proximal contact located more incisally needing more tissue height to fill in and is therefore at a high risk of “black hole formation” (Dhir 2011) (see Figure 5.27a–d). Others also suggested that morphologic characteristics of the periodontium are partly related to the shape and form of the teeth (Hirschfeld et al. 1923; Wheeler 1961 Seibert 1993; Seibert). Weisgold (1977) considered that a long tapering (triangular) crown shape was more suscep- tible to recession, while flat (square) teeth seemed to have greater bands of keratinized gingival, which were more resistant to recession. Olsen and Lindhe (1991) also found that the central incisors with a narrow tooth form had a greater amount of recession when compared to incisors with a square shape.
The contribution of oral hygiene practices to the occur- rence of gingival recession remains a major consideration in our understanding of the etiology, the prognosis, and the treatment. It is important to recognize that gingival recession may be associated with both extremes; poor oral hygiene, and extremely good oral hygiene. In the former type, meticulous brushing is thought to introduce trauma to the gingiva leading to recession (Addy, Mostafa and Newcombe 1987; Niemi, Sandholm and Ainamo 1984). This type of recession is commonly seen on the facial side of canines and premolars and associated with overzealous brushing habits. Poor oral hygiene is associated with reces- sion due to plaque‐induced inflammation and subsequent attachment loss. It appears that many factors related to tooth brushing may contribute to recession. These factors include brushing force and brush hardness, frequency and duration of tooth brushing, as well as frequency of changing tooth brushes and the brushing techniques and types of manual or electric brushes used (Rajapakse, McCracken and Gwynnett 2007). For both overzealous and insufficient oral hygiene, an underlying inflammatory response is likely to contribute to tissue destruction resulting in gingival recession.
On the other hand, Strub, Gaberthüel and Grunder (1991) stated that the keratinized mucosa or dental plaque does not seem to be related to implant failure but that its presence might facilitate the patient’s hygienic procedures. Wennstrom, Bengazi and Lekholm (1994) in his study concluded that the absence of keratinized mucosa was associated with a higher plaque index and gingival index, but not with annual bone loss, while Chung et al. (2006) stated that an increased width of keratinized mucosa around implants was associated with a lower mean alveolar bone loss and improved indices of soft tissue health. Zigdon and Machtei (2008) stated that a narrow band of keratinized mucosa may lead to increased recession, and the absence of adequate kerati- nized mucosa around implants was associated with higher plaque accumulation, gingival inflammation, bleeding on probing, and mucosal recession (Adibrad, Shahabuei and Sahabi 2009). Kim et al. (2009) also sup- ported the fact that decreased keratinized mucosa width was associated with recession and marginal bone resorp- tion. The existence of at least 2 mm of keratinized mucosa was also beneficial for reduced plaque accumulation and bleeding (Schrott et al. 2009). Thus, it was concluded that keratinized mucosa was not a critical factor in the maintenance of interproximal bone, but less keratinized mucosa was associated with more gingival inflamma- tion, plaque accumulation, and recession (Crespi, Capparè and Gherlone 2010).
To establish and maintain an ideal soft tissue archi- tecture, implants should be positioned at the correct distance to the adjacent dentition, at the correct depth, and more palatally positioned (Choquet et al. 2001; Grunder et al. 2005; Kan et al. 2003). When dealing with anterior single implant supported restorations, the thickness of facial bone as well as the dimensions of the facial peri‐implant mucosa are critical for the achieve- ment and long‐term stability of good esthetics, with a reduced risk of future tissue recession (Buser et al. 2004; Grunder et al. 2005). When implants are incorrectly angled or improperly positioned, various prosthodontic techniques have been reported, includ- ing the use of a gingiva‐colored acrylic resin façade, a flexible silicone‐based tissue‐colored material, or removable prostheses (Cura, Saraҫoglu and Cötert 2002; Everhart and Cavazos 1983; Gardner and Stankewitz 1982; Greene 1998).
Juodzbalyus and Wang (2007) stated that a natural buccal and proximal restorative contour can be ensured by correctly orienting the implant in a buccopalatal position. A minimum space of 2 mm should be main- tained on the buccal side in front of the external implant collar surface, and correct three‐dimensional implant positioning has been considered important for long term maintenance of soft tissue levels (Buser et al. 2004). An association of buccal implant malpositioning and mid‐facial recession has been described (Chen et al. 2007, 2009) and should be considered by sur- geons when pursuing immediate implant placement. Studies identified the tooth‐to‐implant distance and the level of the contact point in relation to the bone crest as key factors for maintaining healthy papillae (Lops et al. 2008; Romeo et al. 2008).
It is essential that the clinician is familiar with the various unfortunate clinical situations that may arise due to misplacement and the ways to solve them. The axial misplacement of the dental implant within its hosing can be damaging to the overall health of the soft and hard tissues surrounding the implant, as a resulting deep gingival sulcus with a long junctional epithelium can be a serious consequence due to the fur- ther deep positioning of the implant and the failure of hygiene practice. This creates a favorable environment for several types of bacteria, including anaerobic bacte- ria, to colonize and populate. The deeper an implant is inserted into the bone, the more bone will be resorbed around the implant following second‐stage surgery with an abutment connection. This bone resorption is not a pathological condition but a physiological reac- tion to the implant misplacement. Inflammation and gingival bleeding usually occur as a result of the inac- cessibility for hygiene measures from one side and bac- terial endotoxins from another side. It becomes increasingly urgent to ensure complete removal of the excess luting cement from the interface between the abutment and the restoration. Correction of this clini- cal dilemma is almost impossible to achieve unless supragingival margins of the prosthesis are fabricated.
The failure to position the implant at its optimal depth, such as being placed too shallow, often results in a short crown with constricted margins due to the absence of the “running room.” This makes stacking the prosthetic components supragingival. This clinical predicament is impossible to amend or rectify. The difficulty remains in handling the margins of the final prosthesis and hiding the abutment collar sublingually. In this particular condi- tion, implant removal can be the treatment of choice. The improper mesiodistal positioning of the implant might lead to the total absence of restorative possibilities, and if the implant is placed in the interdental papilla space or is placed too mesialized or leaving no or a minimal space for restoration, it becomes impossible to restore. Violating the labial plate of bone or the labial soft tissues might constitute a major clinical dilemma that is impossible to correct even with the use of the angulated abutments. The consequences of violating the labial plate integrity goes beyond the teeth to the lip support, as it might impinge on lip harmony. Placing the implant angulation in a too‐far lingual position might result in tongue crowd- ing, because to impinge on the tongue space can significantly compromise speech and mastication.
A fair number of clinical approaches have been described to resolve misaligned and malpositioned dental implants if an unfavorable inclination of the implant fixture is the only problem. The use of angu- lated abutments can often improve the prosthetic results of an implant‐supported restoration. Even using the preangulated abutments in too‐far labial implant placement cases will not be effective in most clinical situations because the preangled abutment usually requires a larger restorative dimension than other types and the gingival collar of the preangled abutment will encroach upon the peri‐implant soft tissue and violate its natural contours. The use of the angled abutments will not ensure any protection against recession.
Several factors have been proposed as being important in determining the stability of the peri‐implant marginal mucosa, including the implant shoulder position in a buccolingual and apicocoronal plane (Buser et al. 2004; Garber 1981). In relation to the optimal buccolingual position, Buser et al. (2004) recommended that the implant shoulder should be placed 1–2 mm lingual to the emergence of the adjacent teeth to ensure maintenance of an adequate width of buccal bone and stable mucosa over the buccal implant surface. Evans and Chen (2008) suggested that the buccolingual position of the implant shoulder is a highly significant factor in determining the degree of buccal marginal tissue recession. Implants with a shoulder position at or buccal to a line drawn between the cervical margins of adjacent teeth demonstrated three times more recession than implants with a shoul- der position lingual to this line.
5.3.3.2 The Influence of the Implant Collar Design
The peri‐implant crest module is the collar portion of the dental implant creating a transition zone between the prosthetic part and the implant body. Its design and position in relation to the alveolar crest is critical and its relationship to the abutment implant interface plays a major role in overall harmonious integration and soft tis- sue health. Early tissue breakdown leading to soft tissue and hard tissue loss starts at the crest module. Misch, Qu and Bidez (1999) have studied the influence of the implant crest components and their angulation in relation to the shear and compressive loading. Smooth surface implant collars have been extensively used in past decades; however, a significant drawback of the smooth collar stems from its questionable integration with the surrounding hard tissues. When the smooth collar of an implant is placed under the crest of the bone, increased shear forces are created to the adjacent bone, and eventually bone is resorbed, leading to a marginal bone loss with a long junctional epithelium (Hermann et al. 2001). Hermann et al. (2001) examined the peri‐ implant soft tissue dimensions at varying locations of a rough/smooth implant border in one‐piece and two‐ piece implants in relation to the crest of the bone, when submerged and non‐submerged techniques were employed. Crestal bone changes around two types of implants with varying smooth collar lengths (2.8 and 1.8 mm) were evaluated. Their findings suggest an absence of bone loss was observed when the implants with rough crest modules were placed at the level of crestal bone, exhibiting a shorter (1.8 mm) as opposed to a slightly larger (2.8 mm) machined collar portion.
Weiner, Somin and Ehrenberg (2008) observed that initially the experimental implants showed greater bone attachment along the laser microtextured collar. However, the controls had more soft tissue downgrowth, greater osteoclastic activity, and increased saucerization compared with sites adjacent to experimental implants. There was closer adaptation of the bone to the laser microtextured collars. It was concluded that the use of tissue engineered collars with micro-grooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width (see page 158) (Nevins et al. 2008).
In a clinical study evaluating laser micro-texturing for soft tissue and bone attachments to dental implants, Pecora et al. (2009) incorporated a tapered dental implant (Laser‐Lok surface treatment) with a 2 mm wide collar, to accomplish bone and connective tissue attachment while inhibiting epithelial downgrowth in a prospective, controlled, multicenter clinical trial. A consistent differ- ence in the probing depth between Laser‐Lok and the control implant demonstrated the formation of a stable soft tissue seal above the crestal bone. Laser etched col- lars limited the crestal bone loss to the 0.59 mm range as opposed to the 1.94 mm crestal bone loss reported for the control implant (Elaskary 2009; Pecora et al. 2009; Ricci and Alexander 2001) (see Figure 5.22a and b).
A study of the effect of a machined/rough implant collar on the osseous crest has shown that the least marginal bone loss with each implant occurred when the collar of the implant was placed above the alveolar crest (Alomrami et al. 2005). A change in implant design towards a scal- loped collar to mirror the bone and soft tissue topography with rough surfaces and grooves did not prove to be practical (Wöhrle 2003). Also, it did not show any clinical benefits and made implant position orientation difficult. The last thread location of the implant determines the effective level of remodeling after loading, and this is per- haps even more important than the position of the implant/abutment microgap (Rompen, Touati and Van Dooren 2003). It is the author’s opinion that implants with microthreads reaching the collar do not seem to prevent bone resorption from occurring (see Figure 5.23a and b).
5.3.3.3 The Influence of the Provisional and Prosthetic Designs
The role of interim dental restorations used for optimizing the final result of the restorative and prosthodontic procedures has changed dramatically in the past few years. These restorations are no longer regarded as tem- porary restorations but rather as provisional restorations with distinct functions and purposes. Provisional resto- rations have become a vital diagnostic and assessment tool to evaluate function color, shape, contour, occlusion, periodontal response, implant healing, and overall esthetics. With increased demands placed on provisional restorations, new materials and techniques are being developed and some existing protocols are being refined to accomplish the desired goals. Provisional restorations are often in the oral environment for several weeks, requiring a precise fabrication. An adequate understand- ing of the relationship between periodontal tissues and restorative dentistry is paramount to ensure adequate form, function, and esthetics, as well as comfort of the dentition (Nugala, Kumar and Krishna 2012).
With dental implants, the clinical scenario is signifi- cantly different from that of a natural dentition, with the implant and/or abutment surface being a non‐vital struc- ture without a blood supply. Dental implant design and surface improvements have helped clinicians direct their treatment approach towards a more immediate timeta- ble as well as a more esthetically driven one (Smeets, Stadlinger and Schwarz 2016).
Many factors play a role in the emergence profile: (1) the smoothness and degree of finish of the temporization, (2) venting of the temporization to avoid excessive cement in the gingival crevice, (3) continuous changing of the pros- thetic margins in accordance with soft tissue maturation to provide steady soft tissue support, and (4) the cleanness and purity of the provisional materials. Using the provisional restoration for a sufficient time (four to six weeks) allows the soft tissue to reach its final healing stage and optimal maturation. Then when final prostheses are inserted, mini- mal or no tissue remodeling or migration occurrs.
The prosthetic stage is highly influential in the mainte- nance of peri‐implant tissue stability. It involves, the use of accurate provisional restorations, optimal final prosthetic fabrication, and a precise duration of the provisional resto- ration, which are all factors that need full attention. Implant provisional restorations provide significant and invaluable benefits such as enhanced patient comfort and satisfaction, as well as the ability to contour peri‐implant tissues (Botticelli et al. 2004). This is critical in the esthetic zone, where the contouring of the soft tissues provide an ideal emergence profile to aid in both esthetics and phonetics (Neale and Chee 1994; Chu et al. 2012; Hui et al. 2001).
The interfaces between the gingival unite and the implant collar is mainly composed of the epithelium and connective tissue, which forms the biological width (Abrahamsson et al. 1997; Berglundh et al. 1991; Hermann et al. 2000). The tissue at the most coronal aspect and adja- cent to the implant abutment consists of the free gingival margin, which is covered by stratified squamous epithe- lium. As the epithelium progresses down the implant it becomes non‐keratinized, below the junctional epithe- lium attachment lies the connective tissue attachment (McKinney et al. 1985). Current attention is driven towards the influence of the provisional restorations to the overall stability of the gingival tissues, and the optimal requirements of the provisional subgingival margins were described by (Luchinskaya et al. 2017).
Long‐term use of a provisional restoration should precede the insertion of the final prosthesis. This will help the matu- ration of the soft tissue during the provisionalization stage (Lazzara 1993), thus minimizing the tendency for future exposure of the final implant‐supported components. Especially in the esthetic zone, placing the provisional res- toration for a period of four to six weeks will provide the clinicians with the final mature gingival margin level after soft tissue remodeling has been finalized. In addition, long‐ term temporization will help to guide the soft tissues to mature and remodel, preventing eventual collapse. The rush for premature delivery of a prosthesis will lead to recession of the gingival tissue as the peri‐implant soft tis- sue continues to remodel (see Figure 5.24a and b).
In order to allow stable soft and hard tissue margins around the dental implant abutment, the transmucosal area of the abutment design should not be oversized and expanded but rather stay narrow and concave to thicken and immobilize the circular connective tissue around the connection. This induces thickening of the connective tissue zone, which will ensure long‐term stability of the marginal tissues (Touati, Rompen and Van Dooren 2005) (see Figure 5.25a and b).
The material composition of the implant transmucosal area, surface topography, surface tension, and surface energy have been studied over the years. Gittens et al. (2013) inves- tigated the influence of surface hydrophilicity of titanium implant surfaces on the behavior and differentiation of the epithelial cells. Spriano et al. (2017) suggested that surface hydrophilicity might positively influence the epithelial seal around dental implants. Proliferation, spreading, and mov- ing of the epithelial cells were enhanced on hydrophilic tita- nium surfaces compared with hydrophobic titanium surfaces. In addition, relatively smoother surfaces were pre- ferred (Novaes et al. 2010). Few articles have been found in the literature regarding cell adhesion or cell proliferation on to permanent abutment materials such as titanium, gold alloy, and ceramics (Abdulmajeed and Willberg 2015; Gasik 2016, 2017); however, we are expecting a huge leap in this path to develop in the near future that will help increase peri‐implant tissue stability around dental implant prosthet- ics. The prosthetic margins should be designed to avoid inducing too much pressure to the overlying soft tissues, as any extra pressure induced to the transmucosal area will be translated into apical migration of this tissue, especially in a thin tissue phenotype. The more pressure that is induced, the more liability there is for recession. Labial prosthetic margins should be either equi‐gingival slightly below gingival margin and the abutment shoulder should also be brought up to this level to allow the prosthetic margins to rest on it, leaving the transmucosal area intact and undis- turbed (Neale and Chee 1994) (see Figure 5.26).
5.3.3.4 Miscellaneous Factors
In natural dentition, gingival morphology is partly related to the tooth shape and form (Dhir 2011). Tooth crown morphology can be triangular, ovoid, or square shaped with a long, narrow, or short form. Olson and Lindhe (1991) in their study reported that individuals with a long narrow tooth form demonstrated a thin free gingiva, shallow probing depth, and pronounced scal- loped contour of the gingival margin. Similarly, the tooth shape and form can influence the peri‐implant soft tissue architecture. Tooth shape is one of the five essential diagnostic key factors for peri‐implant esthetics (Garber, Salama and Salama 2001; Kois and Kan 2001). These key factors include the relative tooth position, form of the periodontium, phenotype of the periodontium, tooth shape, and position of the osseous crest. According to Garber et al. (2001), subjects with a long narrow form of the upper central incisors experienced more recession of the gingival margin at buccal surfaces than subjects who had a short wide tooth form. Individuals with square‐ shaped teeth have more favorable esthetic outcomes because of the long proximal contact and less papillary tissue, whereas the triangular tooth shape has a proximal contact located more incisally needing more tissue height to fill in and is therefore at a high risk of “black hole formation” (Dhir 2011) (see Figure 5.27a–d). Others also suggested that morphologic characteristics of the periodontium are partly related to the shape and form of the teeth (Hirschfeld et al. 1923; Wheeler 1961 Seibert 1993; Seibert). Weisgold (1977) considered that a long tapering (triangular) crown shape was more suscep- tible to recession, while flat (square) teeth seemed to have greater bands of keratinized gingival, which were more resistant to recession. Olsen and Lindhe (1991) also found that the central incisors with a narrow tooth form had a greater amount of recession when compared to incisors with a square shape.
The contribution of oral hygiene practices to the occur- rence of gingival recession remains a major consideration in our understanding of the etiology, the prognosis, and the treatment. It is important to recognize that gingival recession may be associated with both extremes; poor oral hygiene, and extremely good oral hygiene. In the former type, meticulous brushing is thought to introduce trauma to the gingiva leading to recession (Addy, Mostafa and Newcombe 1987; Niemi, Sandholm and Ainamo 1984). This type of recession is commonly seen on the facial side of canines and premolars and associated with overzealous brushing habits. Poor oral hygiene is associated with reces- sion due to plaque‐induced inflammation and subsequent attachment loss. It appears that many factors related to tooth brushing may contribute to recession. These factors include brushing force and brush hardness, frequency and duration of tooth brushing, as well as frequency of changing tooth brushes and the brushing techniques and types of manual or electric brushes used (Rajapakse, McCracken and Gwynnett 2007). For both overzealous and insufficient oral hygiene, an underlying inflammatory response is likely to contribute to tissue destruction resulting in gingival recession.
On the other hand, Strub, Gaberthüel and Grunder (1991) stated that the keratinized mucosa or dental plaque does not seem to be related to implant failure but that its presence might facilitate the patient’s hygienic procedures. Wennstrom, Bengazi and Lekholm (1994) in his study concluded that the absence of keratinized mucosa was associated with a higher plaque index and gingival index, but not with annual bone loss, while Chung et al. (2006) stated that an increased width of keratinized mucosa around implants was associated with a lower mean alveolar bone loss and improved indices of soft tissue health. Zigdon and Machtei (2008) stated that a narrow band of keratinized mucosa may lead to increased recession, and the absence of adequate kerati- nized mucosa around implants was associated with higher plaque accumulation, gingival inflammation, bleeding on probing, and mucosal recession (Adibrad, Shahabuei and Sahabi 2009). Kim et al. (2009) also sup- ported the fact that decreased keratinized mucosa width was associated with recession and marginal bone resorp- tion. The existence of at least 2 mm of keratinized mucosa was also beneficial for reduced plaque accumulation and bleeding (Schrott et al. 2009). Thus, it was concluded that keratinized mucosa was not a critical factor in the maintenance of interproximal bone, but less keratinized mucosa was associated with more gingival inflamma- tion, plaque accumulation, and recession (Crespi, Capparè and Gherlone 2010).
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