Introduction:
The routine fixed dental implant prosthesis (FDP) is either a cement-retained crown (using a crown cemented over an abutment into the implant head) or a screw-retained crown (direct prosthetic retention screwed into the implant head). Over the past four decades, implant-supported fixed prostheses (ISFP) treatment has undergone tremendous growth and has become standard dental care. This success is attributed to the immense evolution of implant surfaces and designs, prosthetic components, clinical techniques, and dental materials.
Various clinical and laboratory procedures are involved in the fabrication of implant-supported reconstructions, including numerous decisions related to the use of implant components, materials, etc. During the treatment phase, the clinicians and the technician must decide the retention mode (i.e., screw or cement-retained) since both retention methods have their own advantages and limitations.
What Are the Advantages and Disadvantages of Cement Retained Restorations?
Cement-retained restoration has benefits such as:
- Compensation of improperly inclined implants.
- A passive fit is achieved easily because of the intervention layer of cement between the reconstruction and implants abutment.
- An intact occlusal table is present because of the lack of a screw access hole, and thereby the control of occlusion is easy.
- Cost-effectiveness.
The main disadvantage is difficulty in removing excess cement, which is one of the primary causes for the development of peri-implant mucositis and peri-implantitis.
Advantages and Disadvantages of Screw-Retained Restorations:
Screw-retained fixed dental prostheses (FDP) has the following benefits:
- The retrievability of the reconstructions is more predictable.
- The amount of interocclusal space needed is minimum (about 4 mm).
- Removal of the reconstruction is easy for hygiene maintenance or when repairs or surgical interventions are required.
The disadvantages are:
- The time required for the fabrication is long.
- Expensive.
- Interference of the access hole present in the occlusal table with the occlusion in the posterior sites.
- Cement reconstructions exhibited more biological complications (implant loss; bone loss >2mm), and screw-retained prostheses revealed more technical problems.
Both fixations influenced clinical outcomes in different ways. The screw-retained restoration was more easily retrievable than a cemented one. Therefore, these reconstructions are preferable technically and eventually for their biological compatibility.
What Is Pico Strategy for Cement vs Screw Abutments?
The PICO (population, interventions, comparisons, and outcome) strategy was used by researchers to question and analyze the complications (including technical and biological ) of implant-supported full-arch dentures in patients treated with either screw-retained or cement-retained reconstructions.
- P: Completely edentulous subjects requiring implant-supported full-arch fixed prostheses.
- I: Cement-retained restorations.
- C: Screw-retained restorations.
- O: There is a difference between the technical and biological complications of the screw and cement-retained implant-supported full-arch dental prostheses.
The technical complications include:
- Loss of retention.
- Loosening of occlusal or abutment screws.
- Extensive wear of acrylic resin teeth.
- Fracture or chipping of the veneer.
- Fracture of the implant or abutment or framework or screw.
The biological complications include:
- Bone loss >2 mm.
- Peri-implantitis.
- Peri-implant mucositis.
- General soft tissue complications (including fistula, swelling) and recession loss of the implant.
- Aesthetic complications.
Both types of fixations of the implant-supported prostheses influence the clinical outcomes in their own way. None of the fixation methods are clearly advantageous over the other. Overall, cement-retained prostheses exhibited more biological problems, implant failure, or marginal bone loss than screw-retained constructions.
A high success rate was found in screw-retained cases using all-4 concepts and preferred in full arch restorations. Screw-retained prostheses are easily retrievable; therefore, technical complications can be repaired more easily. This type of rehabilitation also seems preferable from a biological perspective.
What Is All on 4 Concept for Full Arch Restorations?
The all-on-4 concept (Nobel Biocare) is an immediate loading protocol for full-arch rehabilitation of edentulous arches. Four implants (two posterior tilted implants and two anterior axial implants) are placed without any bone augmentation in cases of minimum bone volume. The surgical planning software with cone-beam CT(CBCT) and digital imaging and communications in medicine (DICOM) files from CT scans helps convert data into three-dimensional (3D) images to accurately perform virtual planning of the exact direction and position of the implants.
There are some contraindications to these techniques:
1) In case of a high smile line where bone reduction is necessary in the maxilla or in cases of a thin and irregular crest in the arches, which prevents proper treatment.
2) It provides enough implant and prosthetic space.
Failure of Implant Crown Prosthesis:
The cluster pattern of the implant loss may have been related to the smoking habits of the patients. Titanium frameworks have shown more problems with fracture of veneer compared with gold-alloy frameworks. It has been suggested that an inner-occlusal metal should be delivered on the palatal side for grinding and overloading. Also, increased functional load in the posterior quadrants is an essential factor, which results in implant failure.
Implant failure tends to cluster within-subjects, suggesting that heterogeneous risks may exist among the patient population. Patient-related factors may be a possibility, which would affect the survival of all implants within a given patient population and cause multiple implant failures.
Wearing CDs in the maxilla was associated with more significant implant failure in the mandible due to increased local closing and chewing forces bilaterally in the distal direction of mandibular implant-supported cross arch prostheses occluding with CDs. Masticatory forces are better distributed when the prostheses antagonize nature dentition or a fixed restoration instead of a removable denture. However, a combination of smoking, poor oral hygiene, and a history of periodontitis increases the risk of implant failure. Patients should be informed that smoking during the initial healing phase following implant insertion or a history of significant smoking increases the risk for implant failure.
In the case of cementation of fixed prostheses, proper removal of excess cement is crucial to prevent biological complications. More failure was found in both screw and cement-retained prostheses with metal-resin framework than metal-ceramic or fiber-reinforced acrylic resin bridges. There was a high risk for peri-implant bone loss in the IL-1 composite genotype-positive and smoking patients. Therefore, it is essential to consider the incidence of these kinds of complications during the development of a treatment plan.
Conclusion:
Screw retained restorations are more advantageous biologically than the cement-retained prosthesis. Still, both can fail eventually if there is negligence of oral hygiene or has associated risk factors like smoking habit or local patient factors like heavy masticatory forces and increased functional loads. The dental implantologist or surgeon should consider the necessary elements before planning the treatment for a fixed dental prosthesis (FDP).