First, doctors should assess whether molding would be actively needed after a procedure. For example, a nose ller procedure is one of the most common ller procedures in the nation. In a procedure on a low nose with asymmetry between the nasal bones, there is a big possibility that the nose shape will seem asymmetrical after the procedure no matter how careful the doctor might have been. In such asymmetry cases, doctors should predict that the patient will need correction to some degree after a molding-based procedure. It will be difcult to correct the shape through molding after the procedure is over. Doctors can create a symmetrical shape overall more conveniently by injecting a ller in small doses based on the presence and degree of asymmetry and implementing molding simultaneously from the start.

Second, doctors should consider the degree of external force or facial expression changes to which a ller will be exposed. The bridge of the nose, for instance, can have uneven skin due to facial expression changes in the middle of the forehead and nasal radix and can be pressed by glasses or sunglasses after a procedure. In consultations before a procedure, doctors should predict the possibilities of changing ller shapes due to severe changes to the patient’s facial expressions in the middle of the forehead after a procedure, so they should tell them to the patient. When necessary, they also need to take additional treatment with a toxin on the middle of the forehead and nasal radix before or after a ller procedure, and they should be given explanations and cautions when wearing glasses or sunglasses. When there is high pressure to push down on the skin and soft tissues around a ller injection, the ller will have difculties maintaining its shape right after the procedure due to compression following the procedure. In a nose with a big hollow part, for instance, the compressed area will not

2.6 Considerations forSelecting HA Fillers

revive easily, especially in the nasal radix with the injected ller spreading easily after the procedure. Before a procedure, doctors need to pinch the skin of the compressed part and assess the degree of the skin’s adherence to check the pressure of the skin and soft tissues in the hollow part. If the pressure of the skin and soft tissues is high in the part where a procedure will be implemented, there is a big possibility that the nose shape created by the ller procedure will not last and easily sink due to compression following the procedure. In such a case, doctors should have talks with their patients to choose between a ller that is harder than average to maintain the nose shape created by a procedure even a little bit or a ller of average strength based on a prediction of some sinking and then correction according to the progress.

Finally, doctors should have knowledge about the characteristics of volume changes in each HA ller product they use.

Given the rheological properties, products that are fully hydrated in the manufacturing process swell less by attracting water after an injection. Biphasic llers have their HA molecules entangled tightly with each other structurally and thus attract less water and swell less than soft monophasic llers that have abundance spaces between molecules due to weak cross-linking. Even in the group of monophasic llers, however, some are made hard by causing HA molecules to entangle with each other through active cross-linking. Thus, they have less space between HA molecules and swell less after a procedure than biphasic llers and soft monophasic llers with less cross-linking.

HA ller products mixed with free HA may seem to highlight the initial volume in the early days after a procedure as free HA absorbs water and swells. Free HA is, however, degraded and absorbed a few days after the procedure with only the cross-linked HA components kept. As a result, the ller dose is reduced from the initial injection. Patients may have different reactions to the amount of mixed free HA. In some cases, they are satised with the outcome right after a procedure and complain about the fast speed of the ller fading away as that part may seem even

hollower in a couple of weeks than in the initial state.

HA llers with abundant incomplete crosslinking due to pendant-type BDDEs swell more easily without any special reason than other HA ller products despite similar viscoelasticity and C-MOD, which is the ratio of complete crosslinking provided by the manufacturers. When some products have more serious and persistent swelling than other products and cannot be explained through rheology, doctors should have suspicion about the action of BDDEs based on incomplete cross-linking. The possibilities of delayed immune reactions grow when such products are used in too large doses at a time or in procedures that are repeated too often. Accordingly, it is recommended to have enough observations of clinical progress before deciding to increase the product dose.

2.6 Considerations forSelecting

HA Fillers

2.6.1 Fillers forIntradermal

Injection

The original indication of llers is to supplement dermal deciencies, meaning it is a tool for treating situations where the dermis is decient for various reasons. However, in reality, it has been more widely used for volumization purposes through deep subdermal injection. From the perspective of material saturation, llers tend to expand after injection, typically exceeding the injected volume. Researchers developing llers refer to this as “% saturation”. For example, the phrase “20% saturation” means that after ller injection, the volume increases by approximately 20% by attracting water. While not an ofcial term, it helps understand the properties of llers.

As a result, due to the increase in volume after ller injection, it is easy to experience nodularity when palpating the ller after intradermal injection. As alternatives, methods such as injecting into the subcutaneous fat layer or using less ller than the actual degree of wrinkling have been used. However, recently, methods have been

2 Types ofFillers andRheological Considerations forHA (Hyaluronic Acid) Fillers

developed to reduce the formation of nodules after intradermal injection, such as mixing crosslinked HA with non-cross-linked HA or introducing HA llers with signicantly reduced cross-linking ratios.

These methods are particularly effective for wrinkles around the chin, periorbital wrinkles, perioral wrinkles, forehead wrinkles, etc. In other words, they can be used without the concern of nodularity even for dynamic wrinkles, not just static wrinkles.

2.6.2 Fillers forSubcutaneous

Injection

In the subcutaneous layer of the face, there are often major blood vessels passing through. In particular, as the facial artery transitions into the angular artery, it passes through the subcutaneous layer. Additionally, major blood vessels in the region of the temple are spatially situated in the subcutaneous layer, surrounded by the supercial temporal fascia (Fig.2.57).

Performing procedures without a thorough understanding of the vascular anatomy at the treatment site increases the likelihood of vascular complications. This risk is further heightened when using needles, as they can easily puncture blood vessels. Consequently, deep-layer injections (just above the periosteum) are often recommended as a safer ller technique.

However, although the deepest layers are typically avascular planes, there are situations where subcutaneous layer injections are necessary to achieve precise and optimal ller results. Therefore, avoiding subcutaneous layer injections altogether may not always be the optimal approach.

No matter how sensitive a practitioner’s hands may be, it’s hard to determine the exact depth at which needles or cannulas travel within the subcutaneous layer. Especially feeling the sensation of penetrating through thin facial muscles into deeper layers requires an extremely sensitive touch, which many practitioners may not possess.

Ultimately, during procedures, the depth at which needles or cannulas travel can be condently estimated to be just above the periosteum, at the top of the subcutaneous fat layer, or when injecting into the dermis. When working within the subcutaneous layer, a technique involving the sensation of needles or cannulas brushing against the underside of the dermis at the top of the subcutaneous fat layer is considered a method with a low risk of vascular accidents.

If it’s unavoidable to inject llers into the subcutaneous layer, it’s safest to inject them at the top of the subcutaneous fat layer, just beneath the dermis.

Injecting llers at the top of the subcutaneous fat layer is highly benecial, particularly when treating nasolabial folds. It’s also a helpful injection layer for treating Indian bands.

Skin

Subculaneous fat

Supercial temporal fascia

Deep temporal fascia

Temporalis

Fig. 2.57 Supercial temporal artery course in the temple area. The supercial temporal artery is embedded within the supercial temporal fascia but spatially resides in the supercial fat layer

2.7 Basic Considerations fortheUse oftheHA Filler Degrading Enzyme Hyaluronidase

2.6.3 Fillers forSupraperiosteal Injection

Typically, this depth represents an avascular plane, making it safe for procedures. Therefore, injections are often performed using a cannula or a needle technique involving touching the bone before injection.

However, even in this scenario, absolute certainty cannot be guaranteed. For instance, in areas like the forehead with bony contours, the curvature of the bone may prevent the cannula from maintaining the depth of the deeper layer. Additionally, when injecting ller using a needle technique with bone touch in the temple area, there is a possibility of encountering the deep temporal artery. Furthermore, when injecting after bone touch, there are instances where the needle tip may not remain just above the periosteum but may be displaced into a shallower layer due to the injection process itself, caused by the injected ller.

When injecting into deeper layers, it’s crucial to consider whether the injected ller easily migrates to other areas. For example, when injecting deep-layer llers into the nasolabial area, the ller may migrate to the upper lateral part of the face due to facial expressions, causing the nasolabial fold to appear deeper instead.

2.7 Basic Considerations

fortheUse oftheHA Filler Degrading Enzyme Hyaluronidase

HA llers are dissolved by an enzyme material called hyaluronidase to address side effects or complaints with a shape after an HA ller injection. Hyaluronidase is especially useful in urgent situations where the side effects of an HA ller injection happen in blood vessels.

HA llers should be dissolved by the injection of hyaluronidase after a procedure in the following cases: the ller is not injected in the intended location; the ller is injected too much; there is a huge difference between right and left; the injected ller has moved to a different location;

the ller holds together hard to form a lump or bead; the mass of the injected ller makes it uncomfortable to move the face; the patient has complaints with the shape; the parts around the ller injection are swollen and have inammation due to an allergic reaction; severe inammation and foreign body reactions have caused granuloma; the injected ller is reected bluish on the skin due to the tyndall phenomenon on thin parts of the skin; and side effects with blood vessels are suspected or in progress already due to the injected ller.

“The Right Ways to Use Hyaluronidase to Prevent the Side Effects of HA Fillers” will later discuss the details of how to use hyaluronidase to dissolve an injected HA ller as much as is intended. This section will cover the basic considerations to use hyaluronidase.

First, doctors should consider the dose of hyaluronidase marked in units needed to dissolve an HA ller. In the past, some argued that 150 units or so should be enough to dissolve 1ml of an HA ller according to a calculation of 5~15 units of hyaluronidase to dissolve 0.1ml of an HA ller based on the basic amount of hyaluronidase needed to break the structure of HA molecules. These units may be enough to dissolve to some extent the biphasic llers with a low crosslinking rate or monophasic llers whose ller particles are not entangled with each other too severely in a sticky way due to their weak crosslinking. They are, however, insufcient in completely dissolving HA llers in a hard structure due to the strong entanglement of HA molecules to highlight a lot of volume these days. The researcher uses a minimum of 200~300 units of hyaluronidase to dissolve 1ml of a soft HA ller for wrinkles and 500 units of hyaluronidase or more to dissolve 1ml of an HA ller with reinforced consistency for volume.

Second, it is critical to consider the time for hyaluronidase to take effects. Doctors should rst gure out in advance the differences in reaction time when dissolving biphasic and monophasic llers with hyaluronidase. They must have knowledge about the time it takes hyaluronidase to dissolve the ller of their choice in an emergency where an HA ller should be dissolved

2 Types ofFillers andRheological Considerations forHA (Hyaluronic Acid) Fillers

right away due to side effects in blood vessels. Based on this knowledge, doctors can properly use hyaluronidase according to each HA ller product and obtain optimal results when such side effects happen.

Third, doctors should consider the active duration during which hyaluronidase maintains its effects over time to some extent after being injected into the human body. Based on animal experiments, it has been reported that injected hyaluronidase will maintain its functions for 6h from the injection. There are no particular problems if doctors wait a day on average to repeat a hyaluronidase injection into the HA ller mass or inject a new ller after the old one is dissolved. Once exposed to blood in blood vessels, hyaluronidase will abruptly disappear and within minutes cannot perform its roles. When using hyaluronidase to dissolve HA ller particles blocking a blood vessel, doctors should predict that it will not play its roles any longer than a short period.

Fourth, different criteria should be applied to use hyaluronidase for suspected side effects in blood vessels after an HA ller injection than its injection into a ller mass. When trying to dissolve an HA ller due to side effects in blood vessels, doctors cannot accurately inject hyaluronidase directly into it like when there is a mass. They have to inject widely a hyaluronidase solution in parts where the ischemia of blood vessels is suspected so that it will perme-

ate in blood vessels. Even more amounts of hyaluronidase should be used than the simple dissolution of a ller mass (Fig. 2.58). It is allowed to use up to 1500~3000 units of hyaluronidase at a time. Hyaluronidase will lose its action as an enzyme material much faster inside blood vessels than outside them as it can disappear in 4~5min. Doctors need to check the situations in which blood ows return after the rst injection and repeat an injection in 10~15min when necessary.

Fifth, it is recommended to dilute the hyaluronidase of enough physiological saline before using it and massage the injected area after the injection of a hyaluronidase solution so that it will spread as evenly as possible and increase its contact surface with the ller. As mentioned in the section above, hyaluronidase cannot penetrate into ller particles due to its high molecular weight and can only work on particles directly touching it. As HA chains in contact with the solution are degraded and broken into smaller units, the spaces become larger and work to expand the contact areas gradually. It is important to dilute hyaluronidase in enough amounts of physiological saline in order to inject a hyaluronidase solution evenly and expand the area of ller particles that are in contact with it as much as possible (Fig.2.59).

Sixth, when a ller mass becomes lumpy to form a lump or nodule, the affected areas will

Fig. 2.58 Inltration of hyaluronidase solution through the vessel wall

2.7 Basic Considerations fortheUse oftheHA Filler Degrading Enzyme Hyaluronidase

Fig. 2.59 The action mechanism of hyaluronidase acting on HA ller material

have poor blood circulation. Tissue reactions will become more severe in the collagen capsules enveloping the mass. The capsules on the outside become slightly thicker and form a biolm. In such a case, there will not be enough dissolution on the surface in contact with hyaluronidase, which eventually fails to penetrate the ller mass to dissolve the lump or nodule. When trying to dissolve piles of lumps or nodules in hard collagen capsules for certain, doctors need to inject a hyaluronidase solution into the HA ller mass as

much as possible so that hyaluronidase diluted in a saline can move in between the particles inside the mass rather than on the surface (Fig.2.60).

Finally, a hyaluronidase injection can cause allergic reactions related to allergies such as itchiness and skin are. Doctors should always be prepared for these reactions when using hyaluronidase. Some recommend a skin test before using hyaluronidase. It is a good decision to prepare antihistamine and steroid injections for the treatment of potential allergic reactions.

2 Types ofFillers andRheological Considerations forHA (Hyaluronic Acid) Fillers

Fig. 2.60 Two injection methods of hyaluronidase solution for HA ller mass

The face contains countless vessels, and it is practically impossible to inject llers without damaging the vessels at all. The reason why we should know the vessel structure and positioning relationship of the arteries is to avoid these complications which can lead to skin necrosis and visual complications. Figure3.1 shows the facial supraorbital and supratrochlear arteries which most likely to cause such complications. Of course, if the ller is injected into the supercial

temporal artery, it can reach the ophthalmic artery via the supraorbital or supratrochlear artery, both able to cause eventually visual complications.

The facial artery usually travels upward near the middle of the mandible lower margin and the anterior boundary of the masseter muscle. It is relatively safe to inject ller in the supercial fat layer around the jowl because the vessels are deeply located at the point they pass the mandibular bone (Fig. 3.1a, b). This upward-facing artery can be bent around the corners of the

Fig. 3.1 Arteries of the face

https://doi.org/10.1007/978-981-96-9215-6_3

Fig. 3.2 Vascular structures of the temple

Sentinel

(Zygomaticotem

poral) vein

Superficial layer

deep temporal

fascia (DTF)

Middle

temporal vein

3 Anatomical Considerations forFiller Procedures

Superficial

temporal fat

zygomatic arch

(Red pin)

pad

mouth and can be used to drive up and down the facial muscles. In addition, the ascending facial artery, traveling in and out of the nasolabial folds, produces several branches to the nose and lips. The soft tissue of the lip is soft enough that the pressure is low when the ller is injected, and the abundance of blood supply does not easily cause complications. However, in the case of the nose, the ller injected can increase the pressure in the surrounding tissue, since there is less space to place the ller. Moreover, since the diameter of the facial artery and its branches become narrower as they go up, these vessels can be blocked with less pressure, and the blockage is likely to cause local necrosis around the nose.

Although the facial artery sometimes does not extend the dorsal nasal artery branch as it ascends, the dorsal nasal artery and supraorbital artery from the facial artery is clinically important in causing visual complications by its connection to the ophthalmic artery. It is also important to know the depth at which the arteries are located in order to know which depth is safe to inject.

It is relatively safe to inject ller directly above the bone in the nasolabial area, as the angular artery runs between the subcutaneous and muscular layers. It can also be safer if the physician presses along the course of the artery distal to the injection site using the opposite hand ngers when doing the ller injection, which can prevent the ller from moving up the vessel.

When injecting ller near the eyebrow, one will encounter the supratrochlear artery and supraorbital artery, which originates deep inside the inner part of the orbital rim and rises to the supercial layer. The supratrochlear artery has mainly supercial branches, but the supraorbital artery usually divides into supercial branch and deep branch at a point 1 centimeter above the orbital rim. Unlike a nasolabial fold procedure, this artery produces a deep branch, so the deep layer injection is not necessarily safe. Therefore, pressing the superorbital part of the orbital rim with the opposite hand can prevent the movement of the ller.

Other vascular structures to be kept in mind are the transcanthal vein between the eyes, angular vein located just below the tear trough, and the middle temporal vein which exists between the supercial and deep layers of the temporal fascia in the temple area (Fig. 3.2). Although visual complications via veins are an unusual event, there is an argument that the risk of vascular complications through the vein may be a problem. However, it is impossible to perform the procedure without causing any vascular damage, so you should rst focus much more on avoiding the dangerous arteries and, if possible, then the venous structures.

We don’t need to be too concerned about the nerve structures during ller injection. This is because it is rare to have serious side effects such

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Further Reading