Chapter 4 (Wound Repair)
(1) periosteum, (2) endosteum (3) circulating pluripotential mesenchymal cells
Osteogenic cells (osteoblasts), important to bone healing are derived from what three sources
4 to 6 -- this is recognized radiographically by a loss of a distinct lamina dura.
it is not until ____months after extraction is the cortical bone lining a socket usually fully resorbed
Fibronectin -- Fibroblasts also secrete fibronectin, a protein that performs several functions
what *helps stabilize fibrin*, assists in *recognizing foreign material* that should be removed by the immune system, acts as a *chemotactic factor for fibroblasts*, and helps *guide macrophages along fibrin strands for eventual phagocytosis of fibrin* by macrophages.
Osteo- clasts, derived from monocyte precursor cells,
what are osteoclasts derived from
o Erythema- vasodilation o Edema- transudation of fluid o Warmth- vasodilation o Pain- histamine, kinins, prostaglandins, pressure from edema o Loss of function- histamine, kinins, prostaglandins, pressure from edema
what are the cardinal signs of inflammation (5)
(1) foreign material, (2) necrotic tissue, (3) ischemia, (4) wound tension.
what are the four factors that impair wound healing
(1) inflammation (2) fibroplastic (3) remodeling
what are the processes of *wound healing*
First, bacteria can proliferate and cause an infection in which released bacterial proteins destroy host tissue. Second, nonbacterial foreign material acts as a haven for bacteria by sheltering them from host defenses and thus promoting infection. Third, foreign material is often antigenic and can stimulate a chronic inflammatory reaction that decreases fibroplasia.
what are the three problems associated with foreign material in a wound
primary intention secondary intention
what are the two basic methods of wound healing
(1) vascularity (2) immobility.
what are the two important factors of bone healing
secondary intention
Healing is *slower and produces more scar tissue*----- in primary intention or secondary intention.
stimulates
Placing bone under continuous or repeated cycles of some tension (halts or stimulates) continued osteoblastic bone formation
2 to 3 weeks
Despite the poor organization of collagen, wound strength rapidly increases during the *fibroplastic stage*, which normally lasts how long
plasmin
As fibroplasia continues, with increasing ingrowth of new cells, fibrinolysis occurs, which is caused by _____ brought in by the new capillaries to remove the fibrin strands that have become superfluous
glycosaminoglycans -- Soon, osteoblasts begin to secrete a layer of osteoid over the proteoglycan layer. Bone then forms if proper condi- tions (e.g., no implant movement and good oxygen supply) continue during the months required for healing.
At the implant surface, what secreted by osteocytes coat the oxide layer.
perpendicular -- This is the basis of the functional matrix concept of bone remodeling.
Bone is formed in what direction to lines of tension to help withstand the forces placed on it.
primary -- In both of these situa- tions, *little fibrous tissue is produced*, and reossification of the tissue within the fracture area occurs quickly, with *minimal callus forma- tion*.
Healing of bone by _____ intention occurs when the bone is *incompletely fractured* so that the fractured ends do not become separated from each other ("greenstick fracture"), or when a surgeon *closely reapproximates and rigidly stabilizes the fractured ends* of a bone (anatomic reduction of the fracture).
secondary -- that is, during the fibroplastic stage of healing, a large amount of collagen must be laid down to bridge the bony gap
If a bone is fractured* and the free ends of the bone are *more than 1 millimeter (mm)* or so apart, the bone heals by _____ intention
it tends to pull apart along the initial line of injury
If a wound is placed under tension at the *beginning* of fibroplasia, what happens
wound contraction
In a wound in which the edges are not or will not be placed in apposition, what process diminishes the size of the wound.
(1) a short distance between bone and the implant, (2) viable bone at or near the surface of bone along the implant, (3) no movement of the implant while bone is attaching to its surface, and (4) an implant surface reasonably free of contamination by organic or inorganic materials.
Maximizing the likelihood of bone winning this race with soft tissue to cover the implant requires the what four factors:
*heat* from friction during the cutting process. -- Limiting heat production and rapidly dissipating the heat created at the site help protect the viability of bone along the cut surface. This is accomplished by using sharp bone-cutting instruments, limit- ing cutting speeds to minimize frictional heat, and by keeping the bone cool with irrigation during site preparation. Additional damage to the cut surface of bone may occur if the site becomes infected. This is addressed to some degree by using aseptic surgical techniques, systemic topical antibiotics, or both.
Much of the damage caused by preparing an implant site is the result of what
F-- The greater the amount of available implant surface, the greater is the degree of implant osseo- integration --- Thus, longer or wider-diameter implants and those with sandblasted rather than polished surfaces have more surface available for osseointegration.
T/F-- The greater the amount of available implant surface, the less is the degree of implant osseo- integration
T
T/F-- no wound in skin, oral mucosa, or muscle heals *without scar formation*
T -- This mobility compromises vascularity of the wound and favors the formation of cartilage or fibrous tissue, rather than bone along the fracture line; in a contami- nated fracture, it promotes wound infection
T/F--*excessive* tension or torque placed on a healing fracture site produces mobility at the site.
T
T/F--Bone healing onto the surface of an implant must occur before any soft tissue forms between bone and implant surfaces
T
T/F--Countersinking implants and using low-profile healing screws decrease the ability of any forces to be delivered to the implant.
F--Elastin found in normal skin and ligaments is not replaced during wound healing, so injuries in those tissues cause a loss of flexibility along the scarred area
T/F--Elastin found in normal skin and ligaments *is* replaced during wound healing, so injuries in those tissues cause *NO* loss of flexibility along the scarred area
F--Eventually, once initial inte- gration has occurred, some limited daily pressure on the implant (1000 μm of strain) will actually *hasten* cortical bone deposition on the implant surface.
T/F--Eventually, once initial inte- gration has occurred, some limited daily pressure on the implant (1000 μm of strain) will actually loosen cortical bone deposition on the implant surface.
T
T/F--Implants that are threaded or that otherwise fit tightly into the prepared site are better protected from movement than are nonthreaded or loose implants
T -- Although the living cells in bone die, the inorganic bone structure remains.
T/F--Regardless of how much care is taken to minimize damage to bone during implant site preparation, a superficial layer of bone along the surface of a prepared implant site becomes nonviable as a result of thermal and vascular trauma
T --- If soft tissue arrives first at any part of the implant surface, bone will never replace the soft tissue at that site. If too much of the implant surface becomes covered with soft tissue rather than bone, the implant will not become sufficiently osseointegrated to use for a dental prosthesis.
T/F--The initial deposition of bone must occur before epithelium migrates onto or fibrous connective tissue forms on the implant surface.
T
T/F--The removal of a tooth initiates the same sequence of inflammation, epithelialization, fibroplasia, and remodeling seen in prototypic skin or mucosal wounds
T -- Adherence to surgical principles (see Chapter 3) facilitates optimal wound healing, with re-establishment of tissue continuity, minimization of scar size, and restoration of function.
T/F--The surgeon can create conditions that augment or impede the natural wound repair process.
F--epithelium does not normally contain blood vessels,
T/F--epithelium *normally* contains blood vessels
T
T/F--most injured nerves *spontaneously* recover
osteoblasts and osteoclasts
The events that occur during normal wound healing of soft tissue injuries (e.g., inflammation, fibroplasia, and remodeling) also take place during the repair of an injured bone. However, in contrast to soft tissues, what two cells are also involved to reconsti- tute and *remodel the damaged ossified tissue*.
the third or fourth day -remember, the inflammation stage lasts about 3-5 days
The fibroblasts transform local and circulating pluripotential mesenchymal cells that begin tropocollagen produc- tion on what day after tissue injury
high -- If vascularity or oxygen supplies are sufficiently compromised, cartilage, instead of bone, forms. furthermore, if vascularity or oxygen supplies are poor, the fibrous tissue does not chondrify or ossify.
The fibrous connective tissue that forms in a bony fracture site requires a high or low degree of vascularity (which carries blood with a normal oxygen content) for eventual ossification.
anatomic reduction of the application of bone plates that rigidly hold the ends of the bone together --- this minimizes the distance between the ends of a fractured bone so that ossification across the fracture gap can occur with little intervening fibrous tissue formation
The surgical technique that comes closest to allowing bone to heal by primary intention is what
the rim of fibrous (scar) tissue that remains on the edentulous alveolar ridge.
The only visible remnant of the socket after 1 year post EXT is what
a 2000-Å-thick layer of titanium oxide
The surface of pure titanium implants is completely covered by what. This stabilizes the surface, and it is to this oxidized surface that bone must attach for osseointegra- tion to occur.
fibrin
The principal material holding a wound together during the *inflammatory* stage is ____, which possesses *little* tensile strength
(1) the inferior alveolar-mental nerve, and (2) the lingual nerve
The two branches of the trigeminal *nerve injured most commonly*, for which the altered sensation is clinically significant, are what
(1) healing of bone to the implant (2) healing of alveolar soft tissue to the implant.
Wound healing around dental implants involves the two basic factors:..what are they
80% to 85% -- Because of the more efficient orientation of the collagen fibers, fewer of them are necessary; the excess is removed, which allows the scar to soften
Wound strength never reaches more than what % of the strength of uninjured tissue.
White -- Fibroplasia also begins during the first week, with the ingrowth of fibroblasts and capillaries. The epithelium migrates down the socket wall until it reaches a level at which it contacts epithelium from the other side of the socket or it encounters the bed of granulation tissue (i.e., tissue filled with numerous immature capillaries and fibroblasts) under the blood clot over which the epithelium can migrate. Finally, during the first week of healing, osteoclasts accumulate along the crestal bone.
____ (Red or White) blood cells enter the socket to remove contaminating bacteria from the area and begin to break down any debris such as bone fragments that are left in the socket. (after an EXT)
primary intention --- strictly speaking, healing by primary intention is only a theoretical ideal, impossible to attain clinically; however, the term is generally used to designate wounds in which the edges are closely reapproximated.
define the method of wound healing the edges of a wound in which there is *no tissue loss* are placed and stabilized in essentially the same anatomic posi- tion they held before injury and are allowed to heal. Wound repair then occurs with *minimal scar tissue* because the tissues would not "perceive" that an injury had occurred.
secondary intention
define the method of wound repair implies that a *gap is left between the edges of an incision or laceration or between bone or nerve ends after repair*, or it implies that *tissue loss has occurred* in a wound that prevents approximation of wound edges. These situations require a large amount of epithelial migration, collagen deposition, contraction, and remodeling during healing.
edema
define transudated plasma— aided by obstructed lymphatic vessels—accumulates in the area of injury, functioning to dilute contaminants.
wound contraction.
define A final process, which *begins near the end of fibroplasia and continues during the early portion of remodeling*
Epithelialization (contact inhibition) --- In general, any free edge of normal epithelium continues to migrate (by proliferation of germinal epithelial cells that advance the free edge forward) until it comes into contact with another free edge of epithelium, where it is signaled to stop growing laterally.
define Injured epithelium has a genetically programmed regenerative ability that allows it to re-establish its integrity through *proliferation, migration and contact inhibition*
callus -- During the remodeling stage, bone that was haphazardly produced is resorbed by osteoclasts, and osteoblasts lay down new bone directed to resist low-grade ten- sions placed on the bone
define The *fibroblasts and osteoblasts* actually produce so much *fibrous matrix* in secondary intention healing that the healing tissue extends circumferentially beyond the free ends of the bone
remodeling stage (aka wound maturation)
define The final stage of wound repair, which con- tinues indefinitely
re-epithelialization (i.e., secondary epithelializa- tion)
define an area of oral mucosa is denuded of epithelium (i.e., unattached gingiva) and then left to epithelialize by adjacent epithelium (i.e., attached gingiva) creeping over the wound bed.
tension
define anything tending to hold wound edges apart
ischemia
define decreased blood flow to an area
guided tissue regeneration
define selectively aid the bone-forming process in its race to cover a surface before soft tissue fills the site. the use of woven membranes that have a pore size adequate to allow oxygen and other nutrients to reach the bone grown beneath the membrane while keeping fibroblasts and other tissue elements outside the membrane. By selectively excluding soft tissues, bone is "guided" into a desired position;
tertiary wound healing
define the healing of wounds through the *use of tissue grafts* to cover large wounds and bridge the gap between wound edges.
foreign material -impeded wound healing
define everything the host organ- ism's immune system views as "non-self," including bacteria, dirt, and suture material.
The cellular phase of inflammation is triggered by the activation of serum complement by tissue trauma. Complement-split products, particularly C3a and C5a, act as chemotactic factors and cause poly- morphonuclear leukocytes (neutrophils) to stick to the side of blood vessels (margination) and then migrate through the vessel walls (dia- pedesis). Once in contact with foreign materials (e.g., bacteria), the neutrophils release the contents of their lysosomes (degranulation). The lysosomal enzymes (consisting primarily of proteases) work to destroy bacteria and other foreign materials and to digest necrotic tissue. Clearance of debris is also aided by monocytes such as mac- rophages, which phagocytize foreign and necrotic materials. With time, lymphocytes accumulate at the site of tissue injury.
describe the *cellular phase* of inflammation in wound healing
The vascular events set in motion during inflammation begin with an *initial vasoconstriction of disrupted vessels* as a result of normal vascular tone. The vasoconstriction slows blood flow into the area of injury, promoting blood coagulation. Within minutes, histamine and prostaglandins E1 and E2, elaborated by white blood cells, cause *vasodilation* and open small spaces between endothelial cells, which allows plasma to leak and leuko- cytes to migrate into interstitial tissues. Fibrin from the transudated plasma causes lymphatic obstruction, and the transudated plasma— aided by obstructed lymphatic vessels—accumulates in the area of injury, functioning to dilute contaminants. This fluid collection is called edema
describe the *vascular* events associated with inflammation in wound healing
wound strength increases slowly, but not with the same magnitude of increase seen during the fibroplastic stage
does wound strength increase slowly or fast in the *remodeling stage* of wound healing?
opening is accidentally made into a maxillary sinus during tooth extraction -- If the epithelium of both the sinus wall and the oral mucosa is injured, it begins to proliferate in both areas. In this case, the first free epithelial edge the sinus epithelium may contact is oral mucosa, thereby creating an oroantral fistula (i.e., an epithelialized tract between the oral cavity and the maxillary sinus). Malignant epithelial cells have lost their feature of contact inhibition, showing the value of the contact inhibition process.
give an oral example of contact inhibition
Decreased blood supply can lead to further tissue necrosis and can lessen the delivery to a wound of antibodies, white blood cells, and antibiotics, which thereby increases the chances of wound infection. Wound ischemia decreases the delivery of oxygen and the nutrients necessary for proper healing. Ischemia can be caused by several things, including tight or incorrectly located sutures, improperly designed flaps, excessive external pressure on a wound, internal pressure on a wound (seen, for example, with hematomas), systemic hypotension, peripheral vascular disease, and anemia.
how can ischemia effect wound healing
proliferates across whatever vascularized tissue bed is avail- able and stays under the portion of the superficial blood clot that desiccates (i.e., forms a scab) until it reaches another epithelial margin. Once the wound is fully epithelialized, the scab loosens and is dislodged.
how do *sub epithelial wounds heal*
new capillaries, which bud from existing vessels along the margins of the wound and *run along fibrin strands to cross the wound*
how do new capillaries cross the wound to help vascularize it
secondary intention
how do these wounds heal *extraction sockets*, poorly reduced fractures, deep ulcers, and large avulsive injuries of any soft tissue.
proliferation of epithelium *across the wound bed* from the epithelium contained in rete pegs and adnexal tissues.
how do wounds in which only the *surface epithelium* is injured (i.e., *abrasions*) heal
If sutures are used to pull tissues together force- fully, the tissue encompassed by the sutures will be strangulated, producing ischemia. If sutures are removed too early in the healing process, the wound under tension will probably reopen and then heal with excessive scar formation and wound contraction. If sutures are left in too long in an attempt to overcome wound tension, the wound will still tend to spread open during the remodeling stage of healing, and the tract into the epithelium through which the sutures ran will epithelialize, leaving permanent, disfiguring marks.
how does tension impair wound healing
the socket fills with blood, which coagulates and seals the socket from the oral environment.
how does the tooth socket protect itself after EXT
2-3 weeks
how long does the fibroplastic stage of wound healing last?
*stiff* because of an excessive amount of collagen, erythematous because of the high degree of vascularization, and able to withstand 70% to 80% as much tension as uninjured tissue
how will the wound at the *end* of the fibroplastic stage be clinically (loose or stiff)
it would open along the junction between old collagen previously on the edges of the wound and newly deposited collagen.
if the wound were to be placed under tension near the *end* of fibroplasia what happens
remodeling stage (aka wound maturation)
in what stage of wound healing do *many of the previ- ous randomly laid collagen fibers are destroyed as they are replaced by new collagen fibers*, which are oriented to better resist tensile forces on the wound.
wound contraction
in what stage of wound healing do the edges of a wound migrate toward each other (late fibroplasia and early remodeling)
primary intention
in which method of wound repair does healing *occurs more rapidly, with a lower risk of infection, and with less scar formation*
primary intention
the following heal by what method of wound repair well-repaired lacerations or incisions and well-reduced bone fractures
The first is that its presence serves as a *barrier to the ingrowth of reparative cells*. The inflammatory stage is then prolonged while white blood cells work to remove the necrotic debris through the processes of enzymatic lysis and phagocytosis. The second problem is that, similar to foreign material, necrotic tissue serves as a *protected niche for bacteria*. Necrotic tissue frequently includes blood that col- lects in a wound (hematoma), where it can serve as an excellent nutrient source for bacteria.
what are the two issues of having necrotic tissue in a wound
(1) vascular (2) cellular.
what are the two stages of inflammation involved in wound healing
pain and loss of function
what cardinal signs of inflammation are caused by *histamine, kinins, and prostaglandins released by leukocytes, as well as by pressure from edema.* (2)
swelling
what cardinal signs of inflammation are caused by *transudation of fluid*
Warmth and erythema
what cardinal signs of inflammation are caused by *vasodilation* (2)
tropocollagen, -- The poor orienta- tion of fibers decreases the effectiveness of a given amount of collagen to produce wound strength, so an overabundance of collagen is nec- essary to strengthen the healing wound initially.
what do Fibroblasts deposit which undergoes cross-linking to *produce collagen*. Initially, collagen is produced in excessive amounts and is laid down in a *haphazard manner*.
lag phase -- because this is the period during which *no significant gain in wound strength occurs* (because little collagen deposition is taking place).
what is the *inflammatory* stage sometimes called?
resorb necrotic bone and bone that needs to be remodeled. -- Osteoblasts then lay down osteoid, which, if immobile during healing, usually goes on to calcify.
what is the function of osteoclasts
to repair tissue integrity
what is the purpose of tissue healing
surgeon's goal with respect to scar formation is *not to prevent a scar* but, rather, to produce a scar that *minimizes any compromise of function* and *looks as inconspicuous as possible*
what is the surgeons goal in regards to the scar formation, prevention or minimize damage
*chemical mediators* (released from epithelial cells that have lost contact with other epithelial cells cir- cumferentially) regulate this process, but there is no definitive evidence for this is yet available.
what is theorized to regulate contact inhibition?
physical
what kind of tissue damage include incision or crushing, extremes of temperature or irradiation, desiccation, and obstruction of arterial inflow or venous outflow
chemical
what kind of tissue injury include those with unphysiologic pH or tonicity, those that disrupt protein integrity, and those that cause ischemia by pro- ducing vascular constriction or thrombosis
The second week is marked by the large amount of *granulation tissue* that fills the socket. Osteoid deposition has begun along the alveolar bone lining the socket. In smaller sockets, the epithelium may have become fully intact by this point ---- The processes begun during the second week continue during the third and fourth weeks of healing, with epithelialization of most sockets complete at this time. The cortical bone continues to be resorbed from the crest and walls of the socket, and new trabecular bone is laid down across the socket.
what marks the second week of healing of extraction sockets
Cutting cones (tunneling osteoclasts) move through the bone at a rate of 40 μm per day, removing dead bone and leaving new osteoid.
what moves through the bone at a rate of 40 μm per day, removing dead bone and leaving new osteoid. (after an implant is placed)
cellular
what phase of inflammation is triggered by the *activation of serum complement by tissue trauma.* Complement-split products, particularly C3a and C5a, act as chemotactic factors and cause poly- morphonuclear leukocytes (neutrophils) to stick to the side of blood vessels (margination) and then migrate through the vessel walls (dia- pedesis).
fibroplastic stage
what stage of wound healing do the strands of fibrin, which are derived from blood coagulation, *crisscross wounds forming a latticework on which fibroblasts begin laying down ground substance and tropocollagen*.
inflammation
what stage of wound healing occurs *the moment tissue injury occurs* and, in the absence of factors that prolong this lasts 3 to 5 days.
*cortical bone* (the radiographic lamina dura) covered by *torn peri- odontal ligaments*, with a *rim of oral epithelium (gingiva) left at the coronal portion*.
when a tooth socket is healing what is in the socket after removal of the tooth
primary intention
which method of wound repair lessens the amount of re-epithelialization, collagen deposition, contraction, and remodeling needed for healing
by placement of a layer of epithelium between the free edges of a wound --- Surgeons make use of this phe- nomenon when they place skin grafts on the bared periosteum during a vestibuloplasty or on full-thickness burn wounds.
wound contraction can be lessened, how.