Dental Implants

Anatomy and Physiology

A proper knowledge of anatomical landmarks and its variations prior to implant placement is indispensable to ensure a precise surgical procedure and safeguard the patient against iatrogenic complications. The precise evaluation of distinct anatomical factors such as the position of the mandibular canal, maxillary sinus, the width of the cortical plates, the existing bone density, etc. is very important in appropriate implant selection and planning the most appropriate implant position in the existing clinical condition. Important anatomical structures in the maxilla are a nasal floor, nasopalatine canal anteriorly and maxillary sinus posteriorly. Iatrogenic sinus perforation is commonly encountered complication. This problem can be taken care of by selection of short implants and Sinus lift and bone augmentation procedure.

The most important anatomical consideration while placing an implant in the mandibular arch is the location of the inferior alveolar canal which contains inferior alveolar nerve and artery. Injury to these vital structures during implant placement can cause pain, altered sensation, excessive bleeding, etc. Hence it is important to determine the location as well as the configuration of the mandibular canal prior to implant placement[4][5].

Indications

1. Partial edentulous patients who have intermediate gaps or free-end edentulism (Kennedy class 1).
2. When a patient is not satisfied with the existing unstable and nonretentive conventional complete dental prosthesis.
3.  To preserve existing removable partial prostheses.[6][7]

Contraindications

Absolute Contraindication

Acute illness, the magnitude of defect or anomaly, uncontrolled metabolic disease, bone or soft tissue pathology/infection

Relative Contraindications

Diabetes, osteoporosis, parafunctional habits, HIV, AIDS, bisphosphonate usage, chemotherapy, irradiation of head and neck, behavioral, neurogenic, psychosocial, psychiatric disorders[6][8][9]

Equipment

The armamentarium (comprising equipment and different parts of an implant) used for the surgical placement of a dental implant is as follows:

• Disposable syringes
• Disposable surgical blades
• Towel clips
• Periosteal elevator
• Dental implant surgical kit (containing different drills)
• Physiodispenser with the surgical handpiece
• Dental implant
• Cover screw
• Healing abutment
• Needle holder
• Toothed tissue holding forceps
• Scissors, surgical sutures (in flap surgery)
• Soft tissue punch (for flapless surgeries)

Types of implants and implant materials

• Endosteal
• Subperiosteal
• Transosteal

Endosteal implants pierce only one cortical plate of maxilla and mandible. The most frequently used endosteal implant is root form implant. The subperiosteal implant has an implant substructure and superstructure where custom cast frame is placed directly beneath the periosteum. Transosteal implant crosses through both cortical plates.

Implants can be divided into three materials:

• Metals
• Ceramics
• Polymers

There are three biologic responses when implants are rooted in the host tissue:

• Biotorerant: surrounded by fibrous tissue, e.g., stainless steel
• Bioinert: direct rigid attachment, e.g., titanium and its alloys
• Bioactive: allows the formation of bone on their surface, e.g., hydroxyapatite[10]

Personnel

It is generally accepted that dental implant treatment is done for restorative purposes. The importance of presurgical communication and cooperation between the restorative dentist, periodontist, dental technician, and the implant surgeon is well recognized in modern implantology. The predictable outcome of function and aesthetics of intraoral rehabilitation can and must be determined and controlled before the surgical procedure, with the entire restorative team (the periodontist, surgeon, restorative dentist, laboratory, and patient). Competent interprofessional team-work is essential for the successful completion of implant-retained restorations.[11]

Preparation

The implant placement should be restoration driven to fulfill the patient’s goals. The prosthesis should be designed first, similar to the architect designing a building before making the foundation. Only after the prosthesis is created can the abutments, implant bodies, and available bone requirements be determined to support the specifically predetermined restoration.

The patient is medically evaluated for cardiovascular diseases (hypertension, congestive heart failure, subacute bacterial endocarditis, etc.), endocrine disorders (diabetes mellitus, thyroid disorders, etc.), pregnancy, blood disorders, and bone diseases, etc.[8][6]

 Comprehensive and accurate radiographic assessment provides all necessary surgical and prosthetic information required for the success of the venture. Various types of imaging modalities are used for dental implant imaging:

• Periapical radiography
• Panoramic radiography
• Occlusal radiography
• Cephalometric radiography
• Computed tomography (medical CT and    cone beam CT)
• Interactive CT

CBCT has a great role in dental applications.

Surgical preparation in a standard sterile fashion is recommended for all implant procedures. The goal is to minimize mechanical and thermal injuries to the bone. Osteotomies should be completed under copious cool saline using sharp and new osteotomy drills at high torque and slow speed. Incremental drill sequence should be followed. During an osteotomy, the bone temperature should not exceed 47 degrees to avoid irreversible changes. Bone necrosis and failure of integration can occur when the temperature exceeds 47 degrees C. D1 bone presents the highest risk of overheating.[12][13][14]

Technique or Treatment

Surgical protocols: There are three surgical approaches which are in use over the years: (1) two-stage (2) one-stage, and (3) immediate-loading. The two-stage surgical procedure first places the implant body below the soft tissue until the bone begins to heal (usually 2 to 3 months for mandible and 3 to 6 for maxilla). During the second stage of surgery, soft tissues are reflected to attach a permucosal element or abutment. In one-stage surgical approach, the implant body in the bone and the permucosal element above the soft tissue are both placed simultaneously until initial bone maturation has occurred. The abutment of the implant then replaces the permucosal element without the need for a secondary soft tissue surgery. The immediate-restoration approach places the implant body and the prosthetic abutment at the initial surgery, and restoration (mostly transitional) is then attached to the abutment.

Complications

Various complications and problems can be encountered during surgery and postoperatively. Perforated buccal or lingual plates can be seen during the procedure. In case of an elliptical /eccentric preparation, a wider implant can be used if possible. If not, pack the osteotomy with autogenous graft, compress it, and place implant again. Bleeding in the floor of the mouth can occur from the lingual artery or facial artery injury. So absolute care has to be taken during osteotomy preparation.  Nerve injury can lead to altered nerve sensation in the form of anesthesia, paresthesia or hyperesthesia. Consequently, the surgical landmark is often set conservatively 2mm above the mandibular canal.

The most common postoperative complication is incision line opening. The design of the removable interim prosthesis is involved, it is corrected. The patient is instructed to rinse 2-3 times daily with chlorhexidine. If granulation process extends for more than two weeks, epithelial margin trimming can be done. If implants become exposed during the healing period, no attempt should be made to cover them with tissue. Rather denture is relieved aggressively over the area with implant exposure. The mobility of the implant during healing is unusual but may occur, mostly accompanied by a radiolucent zone around the implant. Whatever may be the cause, the implant should be removed. Signs and symptoms of failure for an implant are horizontal mobility  greater than 0.5 mm, rapid progressive bone loss, pain during percussion, uncontrolled exudate, generalized radiolucency around the implant, more than one half of the bone is lost around the implant and last the implants inserted in poor position, making them useless for prosthetic support. A success rate of 85%at the end of 5 year period and 80% at the end of 10 year period are minimum criteria for success. [15][16][17][18]

Clinical Significance

The goal of modern dentistry is to restore the patient to normal profile, function, comfort, esthetics, speech, and health regardless of the atrophy, disease, or injury of the stomatognathic system.

People are living longer on average. This fact, combined with an existing population of patients with minor and major dental problems, guarantees the future of implant dentistry for several generations of dentists. Dental implants are increasingly used to replace single teeth, especially in the posterior regions of the mouth. Rather than removing sound tooth structure and crowning two or more teeth, increasing the risk of decay, endodontic therapy, and splinting teeth together with pontics, which may have the potential to decrease oral hygiene ability and increase plaque retention, a dental implant may replace the single tooth.

Organized dentistry has finally accepted implant dentistry. The current trend to expand the use of implant dentistry will continue until every restorative practice uses this modality for abutment support of both fixed and removable prostheses on a regular basis as the primary option for all tooth replacements.