Subcrestal Dental Implants

Introduction:

The preservation of bone height for long-term dental implant success is considered a primary pillar for predictable outcomes. When they are placed subcrestally, it can cause the bacterial colonization of dental implants. Due to this reason, this traditional technique is now not followed by most implant dentists necessitating the need for crestal or supracrestal implant positioning.

What Are the Steps Involved in Preoperative Assessment and Anesthesia?

1. The primary step for studying the site of implantation is taking preoperative radiographs. Panoramic radiography or OPG has its own two-dimensional limitations; hence cone-beam computed tomography (CBCT) would be recommended as the radiographic modality of choice.

2. All patients should compulsorily undergo at least one oral hygiene session seven to ten days prior to the implantation procedure. Patients should preferably receive a single dose of prophylactic antibiotics 1 hour prior to the surgical intervention - 2 g of Amoxicillin or 500 mg of Clarithromycin, in patients allergic to penicillin. Patients are asked to rinse with Chlorhexidine mouthwash 0.2% for 1 minute prior to the surgery.

3. Patients are then treated under local anesthesia using Articaine with Adrenaline 1:100,000. No intravenous sedation is required for this procedure.

What Is the Procedure for Placement of Subcrestal Implants?

The two main components of surgery for subcrestal implants are crestal incision and flap elevation. The bone quality is subjectively quantified or diagnosed at drilling as hard, medium, or soft. The implant site is prepared with the standard drill protocol using drills with increasing diameters as suggested by the implant manufacturer. This is done using surgical cutting burs of different lengths and chosen for the patient by the implantologist in the preoperative protocol.

Tapping is used in this procedure in the case of hard bone. Operators are free to use implant of diameters ranging from 3.4 mm, 4.0 mm, 4.6 mm, and 5.4 mm, which are some of the standard diameter sizes according to the clinical indications and operator preference. The neck of the implant is angulated or oriented subcrestally for 0.5 mm or 1.5 mm using a reference point such as the apical peak of the surrounding alveolar bone.

Periapical radiographs are then taken again for assessment of peri-implant marginal bone levels if needed after initial placement. Implants in esthetic areas are preferably submerged, while implants in non-esthetic areas should receive trans mucosal healing abutments.

Non-steroidal anti-inflammatory drugs (NSAIDs), such as Ibuprofen 400 mg, are prescribed to be taken twice a day after surgery as required. In patients with stomach problems or allergies to non-steroidal anti-inflammatory drugs, 1 g of Paracetamol is recommended instead.

What Are the Post Surgery Instructions to Be Given?

1. Patients are instructed to use 0.2% Chlorhexidine mouthwash for at least a minute twice a day for two weeks post the implant surgery and to avoid brushing and possible trauma at the surgical site.

2. A soft diet is recommended for up to two weeks, and avoiding hard or spicy foods is advised.

3. After one week, patients are followed up again to check for implant stability, and sutures are removed.

These subcrestal implants are left to heal and unload for up to three months; eventually, the submerged implants are exposed. The stability of the individual implants can be measured by torquing the abutment screws at a 25 Ncm minimum.

Impressions are taken at this important phase before prosthetic fabrication, and provisional crowns are delivered like provisional titanium abutments.

Periapical radiographs are repeated, and oral hygiene instructions, as well as motivation, should be elaborated by the doctor.

The diameters of healing caps and definitive abutments used are 5 mm for implants replacing posterior teeth like molars, while 3.4 or 4.0 mm usually suffice for implants replacing other teeth based upon the clinicians' evaluation. The provisional restorations are replaced after complete osseointegration in six months by cemented metal-ceramic or standard straight titanium abutments.

Implant stability is assessed while patients must be recalled for follow-up every six months to prevent the risk of peri-implant disease. Dental occlusion is evaluated at each visit.

What Are the Contraindications for Subcrestal Implant Surgeries?

General contraindications to dental implant surgeries

• Immunosuppressed or in cases of immunocompromised patients.

• Irradiation in the head or the neck regions.

• Uncontrolled diabetes.

• Pregnancy or lactation.

• Untreated periodontitis or periodontal disease.

• Poor oral hygiene and poor motivation.

• Substance or drug abusers.

• Psychiatric disorders.

• Unrealistic expectations from implant surgery.

• Acute infection or suppuration at the sites intended for dental implant placement.

• Need for any type of bone augmentation at implant placement.

• Post-extraction sites (sub crestal implants can be inserted only after healing of at least five months).

• Patients unable to commit to follow-up till 5-year-up post-loading.

• Under treatment or with previous treatment with intravenous amino-bisphosphonate drug therapies.

What Is the Possibility of Implant Failure in Subcrestal Position?

Implant or Crown Failures: These biologic or prosthetic complications can occur when there is implant mobility, removal of stable implants that follow the course of a progressive marginal bone loss, or peri-implant infection.

Mechanical complications that can interfere with implant functioning are classified as implant failures. Examples of biological complications are fistula and peri-implantitis. Examples of biomechanical complications are loosening or fracture of the abutment screws.

Conclusion:

From a biological point of view, the placement of the implant borders into a subcrestal location is not ideally recommended. This is so because of the logical dictates of modern implant dentistry and its advances that deem the sensibility to place implants at a depth of 0.5 mm in order to be able to fully use 1 mm more of bone support, especially for situations wherein there is limited bone height.

Ideally, in the placement of dental implants at crestal level or even slightly supracrestally, for the long-term success of implants, the operator studies the relationship between implant positioning depth and esthetic outcomes taking into consideration the clinically relevant criterion. The subcrestal positioning of dental implants through a traditional method is ideally deemed to be successful only when at least it is placed 0.5 to 1.5 mm in healed sites without bearing any clinically appreciable consequences for the patients.