Biological bases in implantology Histology – Anatomy – Physiology

Biological bases in implantology Histology – Anatomy – Physiology

1. PERI-IMPLANT MUCOSA
   • FORMATION OF THE IMPLANT–MUCOSA INTERFACE

Berglundh et al. (2007) described in detail the morphogenesis of the peri-implant mucosa around non-buried titanium implants in dogs:

• Immediately after surgery, a coagulum occupies the space between the implant surface and the mucosa
• during the initial phase of healing, many neutrophils colonize the fibrin clot;
• After 1 week, a few leukocytes are present, but the central part of the clot is occupied by fibroblasts. Their density increases, then, 4 weeks after implantation, it decreases;
• The first signs of proliferation of the junctional epithelium appear after 1 to 2 weeks; it is not fully formed until 6 to 8 weeks.

The junctional epithelium measures between 1.7 and 2.1 mm, 6 to 12 weeks after implant placement;

• The collagen fibers of the connective tissue organized parallel to the implant surface are observed 4 to 6 weeks after implantation and gradually become structured.
• CLINICAL AND MORPHOLOGICAL CHARACTERISTICS

At the end of the healing period, after implantation, the soft tissues around the implant have a shape similar to that of the gum surrounding the tooth.

Clinically, healthy peri-implant mucosa is pink in color and firm in consistency. It forms a collar that encircles the perimeter of the implant abutment.

The boundary between the keratinized peri-implant mucosa and the non-keratinized alveolar mucosa is located 1 to 2 mm from the marginal edge vestibularly and 2 to 4 mm lingually.

The keratinized peri-implant mucosa is anchored to the underlying bone tissue.

The type of mucosa around the implant depends on the distance between the mucogingival line and the alveolar ridge. Since the position of the mucogingival line is genetically determined, resorption of the alveolar ridge thus results in a loss of keratinized tissue.

• As in the periodontal tissues, the peri-implant mucosa, between the abutments of two adjacent implants and/or an implant and a tooth, constitutes the papilla.
• The formation and maintenance of taste buds are influenced by several factors.
• The healthy peri-implant sulcus has a smooth, red inner surface that does not bleed when probed. Its depth varies from 2 to 4 mm and increases with the thickness of

the peri-implant mucosa.

• The primary means of assessing peri-implant health and diagnosing peri-implant diseases is probing. This is performed with a graduated probe (metal or

plastic) and light pressure (0.25 N). The various studies available indicate that peri-implant probing does not damage the tissues although less resistance to the tissues is observed.

• Increasing probing pocket depth over time may be associated with attachment loss and peri-implant bone loss.
• HISTOLOGICAL AND HISTOMORPHOMETRIC CHARACTERISTICS
  • Histologically, the peri-implant mucosa consists of an epithelium and connective tissue.
  • For the peri-implant mucosa, as for the gum around the tooth, we distinguish the oral epithelium, the sulcular epithelium and the junctional epithelium facing the implant.

Epithelium

• The oral epithelium of the peri-implant mucosa covers the coronal parts of the alveolar processes. It is a keratinized stratified epithelium (keratinized mucosa).
• The epithelium–connective tissue union is strong, with numerous deep connective tissue papillae that give the keratinized mucosa great mechanical strength.
• The sulcular epithelium is an extension of the oral epithelium with an average height of 1 mm, varying depending on the depth of the sulcus.
• The epithelium around implants ends at a variable distance from the marginal edge, whereas at the tooth level, the sulcular epithelium ends at the cementoenamel junction.
• This epithelium, derived from the oral epithelium, is a non-keratinized epithelium, due to a subclinical inflammatory state, even in the case of a clinically healthy peri-implant mucosa.
• The junctional epithelium , continuous with the sulcular epithelium, adheres to the surface of the commercially pure titanium implant. It measures 2 mm in length on average and 40 μm in width.
• The junctional epithelium at the bottom of the sulcus consists of 5 to 15 cell layers. The proliferation rate of the junctional epithelium is very high. The most apical cells are located, on average, 1.5 mm coronally from the bone crest.
• The peri-implant junctional epithelium originates from the epithelial cells of the oral mucosa, while that surrounding the teeth originates from the reduced adamantine epithelium, which over the years is gradually replaced by cells of the oral epithelium. Despite this difference in origin, these two epithelia are very similar structurally.
• Peri-implant junctional epithelial cells adhere to the implant surface via a basal lamina and hemidesmosomes (outer basement membrane). A similar structure (the inner basal lamina) is observed at the epithelium–connective tissue interface.
• Compared with oral epithelium, junctional epithelium is characterized by wide intercellular spaces that allow the passage of neutrophils from the connective tissue to the sulcus.
• The junctional epithelium provides a functional seal with respect to the oral environment and the durability of the implant. It is characterized by selective permeability. It is the site of conflicts and/or balance between the attacks of bacterial plaque and the resistance of the peri-implant tissue.

Connective tissue

• The connective tissue surrounding the implant histologically resembles healing tissue.
• Compared with periodontal gingival connective tissue, peri-implant connective tissue is richer in collagen fibers, poorer in fibroblasts, and less vascularized. Collagen fibers are attached to the periosteum and perpendicular to the bone crest. They are not inserted perpendicular to the implant surface, as is the case with dentogingival fibers, which insert at the cementum level. They are organized parallel to the implant surface and align in bundles with a variable path regardless of the type of surfaces (machined or rough).
• At the level of the peri-implant connective tissue, histologically two zones can be distinguished:

• an area near the implants (40 μm) characterized by the absence of vessels, the presence of numerous fibroblasts and circular collagen fibers;
• an area (160 μm) rich in vessels, poor in cells and rich in collagen fibers parallel to the implant surface.

Biological space

• The biological space is the whole represented by the junctional epithelium and the connective tissue. In the case of healthy periodontium, at the level of a tooth, it measures on average 2.5 mm (1.4 mm for the junctional epithelium and 1.06 to 1.08 mm for the connective tissue).
• According to animal studies, the biological space around implants (Implant Brånemark System®) after a 6-month healing period is similar to or slightly larger than that around teeth. It measures on average 3 to 3.5 mm: 2.1 mm for the peri-implant junctional epithelium and 1.0 to 1.5 mm for the connective tissue.

Vascularization of the gum and peri-implant mucosa

PM: marginal edge of the peri-implant mucosa; LAEJ: apical limit of the junctional epithelium; JFP: abutment-implant junction; CO: bone crest; GM: marginal gingiva; JAC: cementoenamel junction.

Namely

The peri-implant mucosa has certain specific characteristics compared to the gum:

• the junctional epithelium and biological space around the implants are slightly longer;
• connective tissue contains fewer fibroblasts and is more fibrous and less vascularized;
• The collagen fiber bundles are oriented parallel to the titanium surface.
• PERI-IMPLANT PHYSIOLOGY PROTECTIVE ROLE
  • The peri-implant mucosa plays a role as a protective barrier against the oral environment, the junctional epithelium around the implants being a functional seal
  • like around a tooth. In addition to its sealing role, the junctional epithelium also plays the role of “mediator” of the host’s response to bacterial aggression at the sulcus. It allows neutrophils to pass through, constituting the first line of defense from the connective tissue to the sulcus, and its cells respond to different stimuli.
  • Although the peri-implant mucosa has certain specificities compared to the gingiva that could make it more susceptible to bacterial attacks, the response to dental plaque of peri-implant tissues is similar to that of periodontal tissues. Dental plaque bacteria that colonize the implant surface cause neutrophils to migrate to the sulcus and form an inflammatory cell infiltrate.
  • Histologically, an inflammatory infiltrate is observed even within healthy peri-implant mucosa in response to plaque bacteria. For some authors, this infiltrate is located more particularly at the implant-abutment junction, and it is centered on the junction.
  • The imbalance between bacterial load and host defense capabilities is the cause of peri-implant diseases. Like periodontal diseases,
  • Peri-implant diseases are divided into two clinical entities, peri-implant mucositis and peri-implantitis.
  • Peri-implant mucositis is an inflammatory process that affects only the soft tissues around a functioning implant;
  • Peri-implantitis is an inflammation of the mucosa associated with peri-implant bone loss.
  • Like periodontal disease, poor oral hygiene leads to the accumulation of plaque and promotes the development of peri-implant diseases.

2. PERI-IMPLANT FLUID
   • Gingival fluid appears in the sulcus as an inflammatory exudate. The volume and composition of gingival fluid depend on the peri-implant health status.
3. CLINICAL CONSIDERATIONS KERATINIZED MUCOSA
   • The need for keratinized mucosa around implants is a matter of controversy.
   • The presence of keratinized mucosa does not appear to be essential for maintaining peri-implant health. Healthy non-keratinized mucosa is observed around implants.
   • However, a reduced area of ​​keratinized mucosa or its absence is associated with: plaque deposits, mucositis, recessions and, for some authors, crestal bone loss.
   • Mucosal thickness appears to be more important than height. It is often recommended to surround implants with a “firm” keratinized mucosa instead of a “mobile” alveolar mucosa to improve their long-term prognosis.
   • Gingival grafts are proposed but there is insufficient scientific evidence to conclude whether increasing the volume of keratinized mucosa is of benefit.

GINGIVAL BIOTYPE

Depending on the gingival and bone morphology, two biotypes are distinguished:

• the thin biotype: thin gums, elongated teeth, long and thin papillae;
• the thick biotype: thick gums, short teeth and short, wide papillae.
  • Clinically, the parameter that allows the presence of a thin biotype to be demonstrated is the visibility of the body of the probe through the sulcus.
  • The importance of biotype in maintaining peri-implant tissues remains controversial. It has been described that if the crestal mucosal thickness before implant placement is less than or equal to 2 mm, crestal bone loss of 1.45 mm could occur at 1 year around implants placed juxta- or supra-osseous. A minimum thickness of the peri-implant mucosa is often recommended.
  • To reconstruct the volume of the peri-implant mucosa, connective tissue grafts are then proposed. Indeed, the biotype as well as the height/thickness of the keratinized mucosa are factors to consider for the long-term outcome, although their roles are not fully specified.

TOPOLOGY AND CLINICAL CONSIDERATIONS OF THE EDENTULOUS SITE

• Tooth extraction causes significant tissue changes inside and outside the alveolus. The alveolar processes are particularly fragile and labile.
• Following avulsion, the shaping/reshaping process results in their resorption.
• This resorption is partly explained by the absence of physical constraints linked to the absence of function. In particular:

• resorption of the vestibular wall is more pronounced than that of the lingual wall;
• the center of the crest, following remodeling, moves palatal and lingual;
• the top of the vestibular cortex is systematically located more apically than the top of the lingual cortex;
• The amount of bone loss was estimated at 30% at 3 months post-avulsion and 50% at 6 months post-avulsion.
  • Generally, the buccal bone is thin, while the lingual bone is rather thick.
  • Between the two cortices, the cancellous bone consists of lamellar bone. Generally, edentulous sites contain more cancellous bone in the maxilla than in the mandible.
  • Following tooth avulsion, in some extreme cases, the entire alveolar process may be lost. In this case, only the basal bone remains at the base of the site.
  • Classification of residual bone. Lekholm and Zarb (1985) classified residual bone from the edentulous site according to volume into five groups:
• in groups A and B, bone of the alveolar process remains;
• while in groups C, D and E only a small amount remains
• These authors also classified the residual bone of the edentulous site into four classes based on “bone quality”:

• class 1: the residual bone is made up almost entirely of compact bone;
• class 2: cortical bone is thick and cancellous bone volume is low;
• class 3: cortical bone is thin and trabeculated cancellous bone is dense;
• class 4: cortical bone is thin while spongy bone is more prominent
  • The healed edentulous site is covered with masticatory mucosa 2 to 3 mm thick.

mm. Histologically, it consists of connective tissue (lamina propria) and stratified epithelium. The connective tissue is rich in fibroblasts and dense with collagen fibers organized into bundles. The mucosa adheres to the bone with the periosteum.

• The edentulous site may be covered with keratinized or non-keratinized mucosa,

• depending on the extent of bone resorption;
• the gingival biotype;
• mandibular or maxillary location;
• location in the arch (anterior or posterior sector);
• the location of the mucogingival line;
• the depth of the vestibule.

4. Anatomical obstacles:

The nasopalatine or incisive foramen The infraorbital foramen

The greater palatine foramen The maxillary sinus

The nasal cavities

The mandibular foramen The inferior alveolar canal The mental foramen

The mandibular incisive canal

The lingual foramen and lateral canals

Biological bases in implantology Histology – Anatomy – Physiology

  Wisdom teeth can cause pain if they erupt crooked.
Ceramic crowns offer a natural appearance and great strength.
Bleeding gums when brushing may indicate gingivitis.
Short orthodontic treatments quickly correct minor misalignments.
Composite dental fillings are discreet and long-lasting.
Interdental brushes are essential for cleaning narrow spaces.
A vitamin-rich diet strengthens teeth and gums.
 

Biological bases in implantology Histology – Anatomy – Physiology