Implants in Maxillofacial Prosthesis

Introduction

Face identification establishes personal recognition. A person's well-being may be negatively impacted by facial malformations or abnormalities. These deformities can be congenital, caused by malformation and developmental disturbances, or acquired, caused by pathologies such as necrotizing diseases and onco surgeries or trauma. The primary aim in rehabilitating the maxillofacial defect patients is to restore the function of mastication, deglutition, speech, and to achieve normal orofacial appearance.¹ Reconstruction of facial defects can be done either surgically or prosthetically or combination of both, depending on the site, size, etiology, severity, age and the expectation of the patient.² The current Glossary of Prosthodontic Terms - GPT 9 defines maxillofacial prosthetics as, "the branch of prosthodontics concerned with the restoration and/ or replacement of the stomatognathic (jaws) and craniofacial (facial) structures with prostheses that may or may not be removed on a regular or elective basis."³

Classification of Maxillofacial Prosthesis

a. Intra oral prosthesis

i. Maxillary defect

a. Hard palate: Surgical obturator, Interim obturator Definitive obturator

b. Soft palate: Speech appliance, Meatus obturator, Palatal lift prosthesis

ii. Mandibular defect: Mandibular resection prosthesis, Guide flange prosthesis

iii. Glossectomy: Tongue prosthesis, Palatal augmentation

iv. Splints/ Stents: Surgical splints, Bite splints, TMJ appliance

b. Extra oral prosthesis

i. Orbital

ii. Nasal

iii. Auricular

iv. Mid-facial

c. Combination

i. Orbito-maxillary

ii. Naso-maxillary⁴

Large facial deformities are challenging to treat prosthetically due to the lack of anatomic undercuts, constrained retention choices, soft tissue mobility, and the weight of the prosthesis.⁵ A multidisciplinary approach is required to maintain proper prosthesis retention, especially when the defect is large. With the advent of anticipated osseointegration, a new era in prosthodontic rehabilitation of the head and neck area began. Cases that were previously deemed "hopeless" were offered a fresh range of alternatives and the possibility to be fully restored to form and function.

The retention of maxillofacial prosthesis is significantly more difficult when ablative surgery is followed by radiation therapy. In such cases, implants have been demonstrated to be a practical method for enhancing prosthesis retention and patient comfort. The type of the defect should be recognized, and implant positioning should be planned to use the favorable anatomic structures. This article review covers the fundamentals and biomechanics of craniofacial implants as well as design issues, implant systems, and prosthetic attachments.

Implant Retained Maxillofacial Prosthesis

Craniofacial implants

Endosseous implants may be used as an alternative anchorage system for the diminished retention, stability and support. They can be used in edentulous and partially edentulous jaws, can be used for congenital, developmental, traumatic defects.⁶ The earliest abutment employed was also an intraoral type, but as time passed on, extra-oral abutments of various types were produced. Abutments for bone-anchored hearing aids (BAHA) and abutments for bone-anchored epithesis are two examples (BAE).⁷

Principles of craniofacial implants

The proper patient selection, biomechanical planning for prosthesis fabrication, and application of biomedical principles are the cornerstones of biomedical principles.

Principle 1: Avoid tissue injury. Most materials used in maxillofacial prostheses are biocompatible with skin and mucous membranes.

Principle 2: Esthetic retention. The patient's appearance must be restored to something close to "normal."

Principle 3: Retention for function. The patient's survival as well as overall recovery depends heavily on their ability to breathe, chew, swallow, and speak.

Principle 4: Retention for prevention. In patients undergoing postsurgical and radiologic cancer rehabilitation, decubitus ulcers will be avoided because of the stable retention of epithesis and prostheses in rest and function made possible by osseointegration of titanium fixes.

Principle 5: Maximum direct bone transfer loading. Direct bone loading by osseointegration will promote bone remodeling and stop bone resorption.

Principle 6: Combined direct bone and soft tissue transfer loading or retention. In major deficiencies involving movable structures in the head and neck region, it is necessary to transmit the load to sustain the epithesis or intraoral prosthesis on the adjacent soft tissues. This combined method enhances prosthesis and epithesis retention.

Principle 7: Patient's psychological and social rehabilitation.⁸

Implant sites: Intra oral

Residual premaxillary: For most maxillectomy patients, the remnant pre-maxillary segment is the best location for implants as the anterior maxillary segment lies opposite the most retentive section of the defect, which is found along the posterior lateral wall. Premaxilla has sufficient volume and density of bone; thus every effort is made to maintain this segment of bone as much as feasible.

Maxillary tuberosity: If bone is insufficient in the residual pre-maxilla, then maxillary tuberosity is considered. But bone-implant contact those forms in the maxillary tuberosity is not very dense, therefore it may not assure a predictable outcome. Some clinicians have advocated inserting lengthier and mesially tilted implants in the pterygoid plates. If there is at least 10 mm of bone underneath the maxillary sinus, the edentulous posterior alveolar process can be used as an alternative location for implants.

Sinus lift with autogenous bone transplant is becoming more popular, but its predictability in patients with maxillary defects is yet to be confirmed.

Residual elements of zygoma: The zygomatic implant was created by Branemark to address the lack of maxillary bone support for prosthetic rehabilitation. It is characterized by a lengthy (30-62.5 mm) implant that receives its primary anchoring from the zygoma bone in the presence or absence of maxillary alveolar bone. The head of the zygoma implant has been developed to allow prosthesis connection to reduce the complications of various angulations.⁸

Types of Osseo integrated Implant Used in Maxillectomy Patients

1. Conventional dental implants: Traditional implant anchorage sites are constrained by tissue resection or loss, may be impacted by tissue bed radiation, and may even be restricted in ways that obstruct appropriate anterior-posterior spread and cross-arch stabilization.

2. Zygomatic implants: The zygomatic implant was created by Branemark to address the lack of maxillary bone support for prosthetic rehabilitation. It is characterized by a lengthy (30-62.5 mm) implant that receives its primary anchoring from the zygoma bone in the presence or absence of maxillary alveolar bone. The zygomatic implant requires a trans-sinus technique to gain intraoral access to the zygomatic buttress.

3. Mini dental implants: These implants placed at the time of the ablative surgery will shorten or hasten the recovery process of the edentulous patient as the obturator will be more efficacious.⁸ (Figure 1).

Implant attachments

Magnets, clip-bar systems, and milled-bar prostheses are a few retention methods for implant-retained maxillary obturators. Because of the limited vertical space offered by the site of implants, extra-coronal resilient attachment (ERA) and O-ring attachments are used.

Magnet attachment: These are tiny in size, allowing it to be inserted into a maxillary prosthesis without obstruction. It also has enough attracting force (7.2 N) to prevent prosthesis displacement. Magnets also produce low lateral strains which improve implant success.

Magnets have drawbacks such as low corrosion resistance and possible harmful effects which may limit their usage in the oral environment. However studies show that this bad effect is not seen clinically (Figure 2).

Stud attachment: Because of the smaller vertical space requirement afforded by the position of implants, and the unique bar design, and the need to produce a harmonious path of insertion, stud attachments, ball, locators, and ERA attachments promote retention of the obturator (Figure 3).

Bar attachment: Maxillary obturator sustained by milled bar attachments greatly enhances prosthesis retention. Bar attachment is employed to splint implants supporting obturators for edentulous maxilla with no documented complications. These implants are subjected to high amounts of stress, which may alter bone and cause loss in skeletal support.⁹ (Figure 4)

Implant sites: Extra oral (Figure 5)

Craniofacial implants are categorized as (1) alpha, (2) beta, or (3) gamma sites based on the quantity of bone accessible for implant fixture placement.

Alpha site: The amount of bone available at these sites is considerable, ranging from 6 mm to greater. Bone is more resistant to loads and regular fixings. These can be used to keep complex face or dental prostheses in place. The alpha sites in the craniofacial region are the zygoma, anterior maxilla, and mandible.

Beta sites: They can be located in the periorbital area, as well as the temporal, zygomatic, and anterior nasal fossa. Short dental fixtures (5 mm) or flanged fixtures are used (4 mm).

Delta sites: The buttress, pyriform, zygomatic arch, medial orbit, temporal and frontal bones, and zygomatico-frontal process are all delta sites. 3 mm or smaller implant fixtures are employed.⁸

Characteristics of Extraoral Implants

These implants are shorter than oral implants, constructed of titanium alloys, measuring 3-5 mm in length, threaded, and have the same machined surface. V-form, square, buttress, and reverse buttress are the four thread forms recommended for implants. V- shape is the most often utilized thread design for endosseous intraoral implant. However, it is not suitable for short implant lengths. Buttress thread forms are thought to be better for supporting maxillofacial prostheses. Tensile and compressive forces act on the implant during normal prosthesis removal and reinsertion. Compressive stresses are successfully resisted by bone; however tensile forces might be harmful. Because the outward thread face is flat, the reverse buttress thread form can take care of the draw out force to a higher extent.

Reverse buttress thread shapes can be utilized to support a maxillofacial prosthesis. Extraoral implants are less diversified than intraoral implants. These are smaller in size and feature a dual structure with an endosseous portion and a thread in the abutment.⁹

Branemark Implant

The Branemark system was the first extra orally implanted system.¹⁰ They are self-tapping implants. Titanium screws with lengths of 3, 4 mm and 5.5 mm are offered for the extraoral area. The Cochlear Company is currently marketing the Branemark system under the Vista fix brand.

ITI System

A sand-blasted, large grit, acid-etched surface, known as the SLA surface, was debuted with ITI implants (International Team for Implantology) marketed by the Straumann. Their roughness is two-staged, with a coarser roughness of around 20 m being layered by a finer roughness of 2 micron intervals.¹¹ Self-tapping titanium screws with a diameter of 3.3 mm and a countersunk depth of 3.5 or 5 mm with a coned seat and a diameter of 2.5 or 4 mm with flange for the extraoral region. The hydrophilic SL Active surface is also available on the longer screws meant for the extraoral region.¹²

Grouped implants

Epitec system: The system consists of self-tapping 2 mm titanium screws in lengths of 4.5 and 6 mm, a moldable quadratic titanium grid with 16th read holes, and the so-called 3D carrier plate. The 3D carrier plate must be cut into the proper shape. For stability purposes, it is necessary to retain as many connecting bridges as feasible between the single screw holes. The main factor in plate retention is the use of mono cortical bone screws. Bone will also cover the 1 mm thick connecting bridges of the 3D carrier plate (Figure 7).

Epipalting system: It is an adaption of Medicon's 2.0 titanium mini-plate system which is utilized in the firled of Anaplastology. Implants for the auricular, orbital, and nasal regions, as well as a universal plate are available. The Epiplating system's titanium plates are 1 mm thick but 2 mm wide, making them stronger than the Epitec grid system. The thickness of the plate in the area of the tapped holes provided for the mountings is 2 mm, which is appropriate for 4th read turns and counterbalances any propensity of the percutaneous base posts or magnets to loosen. Titanium screws with a width of 2 mm are used to secure the plates, and are available in the following lengths: 4-, 5.5-, and 7-mm. The plates are more resistant to rotating stresses which occur when screwing down and unscrewing the mountings. This can be used in conjunction with the BAHA system's hearing device abutment.¹² (Figure 7)

the skin is then dressed in gauze soaked in ointment to protect it. In a two-stage procedure, two surgeries are performed. The initial treatment involves implant insertion in the desired site of the craniofacial deformity. After an adequate period of osseointegration and healing, the second stage operation is carried out. This procedure included subcutaneous tissue reduction, healing caps over the abutments, and gauze soaked in ointment to lessen postoperative hemorrhage and swellings.¹⁰

Surgical template

Because it enables comparison of the pre- and post-operative implant location, a computerized surgical template is preferred to a manual surgical guide. Maxillofacial prostheses can now be designed digitally, thanks to recent developments in computer technology. A number of tools have been created to help surgeons with digital planning of extraoral implants, including robot-assisted craniofacial implant placement and implant placement with image guidance. Digital surgical guides are created using CAD-CAM, quick prototyping, computed tomography, cone-beam computed tomography, and other technologies.¹¹

Craniofacial reconstruction with extraoral implants Auricular

Congenital defects, trauma (burns, accidents, animal attacks, and human bites), or surgical removal of cutaneous malignancies are the most common causes of auricular defects.

Major cancer resection, radiation therapy, severely weakened local tissue, failed autogenous reconstruction, patient preference, and poor operational risk are all indications for the auricular prosthesis. Microtia and calcified costal cartilage are all relative signs.

Auricular prosthesis implant location and number: The implants are to be 15 mm apart in the mastoid area, 20 mm away from the auditory canal entrance, according to the established protocol. Two implants are usually enough to support an auricular prosthesis, and they should be put at 8 and 11 o'clock on the left side, as well as 1 and 4 o'clock on the left side.

Bar and clip, ball clips, and magnetic retentive cap systems are the retentive mechanisms used. The recovery time is usually 3 to 4 months.^10,11

Orbital prosthesis

These are prescribed for individuals who have lost or are missing an eye because of a congenital defect, irreversible trauma, malignancy, severe blindness, or sympathetic ophthalmic.

Implants are placed on superior orbital rim and outer or inner canthus. A second or two implants are frequently implanted in the inferior orbital rim or zygoma. The implant utilized is usually 3-4 mm in length. To allow for hygiene, there should be a 10-12 mm gap between the implants. Magnets are the most often used retentive mechanisms with implants. The recovery time is usually 6 to 8 months.

Non-integrated (e.g., PMMA and Silicone implants), semi-integrated (Allen implants), integrated (Cutler's implants) implants, bio-integrated (Hydroxyapatite, structures with or without integration Porus polyethylene, with the prosthesis Aluminum oxide) implants, and biogenic implants (Dermis-fat graft the prosthesis Cancellous bone) are all used in orbital prosthesis.¹²

Nasal prosthesis

Osseointegrated nasal reconstruction is indicated in failed autogenous reconstruction, scarring at autogenous donor sites, and removal of sufficient reconstruction due to tumor recurrence. The floor of the nose, piriform ridge, inferior orbital foramen and glabella are the most common implant insertion sites.

Implant length of 4 mm or longer fixtures are used. When supporting both intraoral and extraoral prostheses, 7-10 mm are employed. These implants are referred to as bifunctional implants because they may support both oral and extraoral prostheses. Implants should be spaced 8 to 10 mm apart in the anterior region of the nasal floor to allow for attachment to immovable tissues. The recovery time is 6-8 months. Mini magnets (primarily) and bar and clip retentive devices are utilized.^12,13

Benefit over Traditional Maxillofacial prosthodontists (MFPs)

The prosthesis's retention and stability have improved. Adhesive skin responses are no longer an issue. Prosthesis placement is easier and more accurate. Patient comfort and improved skin hygiene has been achieved. Reduced adhesive removal and reapplication maintenance on a daily basis, increased prosthesis longevity are noted. Enhances the appearance of the lines where the prosthesis meets the skin.¹⁴

Discussion

Extra oral implants have a high survival rate, making them the safest, most reliable, and most effective way to keep maxillofacial prostheses in place. This increases patient comfort and eases maintenance. The technology is highly adaptable to various circumstances, and the technique utilized can be adjusted to address the plethora of issues while also boosting patient trust.

Conclusion

Extra oral implants have a high survival rate, making them the safest, most reliable, and most effective way to keep maxillofacial prostheses in place. This increases patient comfort and eases maintenance. The technology is highly adaptable to various circumstances, and the technique utilized can be adjusted to address the plethora of issues while also boosting patient trust.

Conflict of interest

None