A Technique for Prosthetically Aligning Multiple Non-Parallel Implants
Mohamed Moataz Khamis, BDS, MS, PhD1,Khaled Mohamed Farrag,BDS2 ,Niveen Hazem Zakaria, BDS2
1Professor and Chairman, Prosthodontic Department, Faculty of Dentistry, Alexandria University, Alexandria, Egypt.
2Demonstrator of Fixed Prosthodontics, Conservative Dentistry Department, Faculty of Dentistry, Alexandria University, Alexandria, Egypt.
Received Date: 07/03/2022; Published Date: 12/04/2022.
*Corresponding author: Mohamed Moataz Khamis,Professor and Chairman, Prosthodontic Department, Faculty of Dentistry, Alexandria University. 20 Amin Fekry Street, El-Raml Station, Alexandria, Egypt (203) 4865416
Aim and Objective: A device was designed to be used together with a dental surveyor to determine the proper abutment angle combination in cases with multiple non-parallel implants
Background: Anatomical and technical difficulties may lead to unfavorable implant positioning and/or alignment. Angled abutments can be used to properly align non-parallel implants. Determining the required abutment angulation can be challenging especially with multiple implants.
Technique: An implant level impression is made and poured. Long impression posts are screwed onto the implant analogs to determine implant alignment. The cast is placed over the device platform that is placed over a dental surveyor. The angulation between implants is determined by aligning the long impression posts to the analyzing rod of the surveyor and the implant angulation is measured using the device.
Conclusion: This simple device determines the angle between multiple implants to achieve a common path of insertion for splinted multiunit restorations.
Keywords: Abutment angle determination; dental implants; unparallel implants; angular deviation.
Placing implants in a proper prosthetic position and direction is essential to achieve a successful long-lasting restoration.1 However, this is sometimes difficult to achieve because of anatomical or technical difficulties and angled abutments are required to correct the unfavorable alignment.2,3
Angled abutments can either be custom made or prefabricated.2,3 When custom made abutments are used, proper abutment angulation can be achieved by using either conventional techniques or a computer aided design software.4 Prefabricated abutments whether screw or cement retained are provided in different angles to be selected according to implant angulation.5 Selection of proper abutment angulation can be performed by using trial abutments that are provided in different angles by some companies to be tried on a cast or intraorally.6
Challenging situations arise when multiple nonparallel implants are to be restored. The selection of the proper combination of abutment angles to ensure a single path of insertion for a splinted restoration becomes a challenge. Attempts have been made to measure the angle between adjacent implants using panoramic x-rays or by digital photographs and plane geometry.7 However, the angle was only determined in 2 dimensions.1,8 Accurate measurements have also been made by using cone beam computed tomography scans. However, this necessitates exposing patients to unnecessary doses of radiation.8-11 This article presents a simple technique for determining the prosthetic angle of single or multiple implants for appropriate abutment selection. A device was designed and fabricated to aid in this procedure.
- The abutment angle determining device (ADD) consists of a platform 10 cm in length and 8 cm in width mounted on 4 legs, each 5 cm in length. The platform has a horizontal top verified by a water balance scale. It carries a rotating base that moves in a hinge motion. On one side of the platform, a protractor is attached with its 0-mark corresponding to the top surface of the hinged base. The base moves in an upward and downward hinge motion by clockwise rotation of a screw (4.5 cm in length) passing through the lower surface of the device platform (Fig. 1).
- Make an implant level impression and pour by using dental stone. Attach long impression coping posts to the implant analogs as seen in Fig. 2. Select the most properly aligned implant (R) in relation to the rest of the teeth in partially edentulous situations or in relation to the rest of implants in edentulous cases. The implant (R) will be considered the reference to which the other implant angulations will be correlated and measured (Fig. 3).
- Position the cast on the movable base of the ADD. Make sure the base is set at the zero mark of the protractor by rotating the bottom screw completely in an anticlockwise direction.
- Place the ADD over the surveying platform of the surveyor (Ney surveyor; Dentsply International Inc.). Attach an analyzing rod to the tool holder (Fig. 4).
- Trim the base of the cast to align the long axis of the reference implant (R) to be parallel to the analyzing rod in mesiodistal and buccolingual directions (Fig. 5).
- To measure the angle between the rest of the implants and the reference implant (R) in a mesiodistal direction, align the cast on the ADD so that the facial or lingual surface of the neighboring implants are parallel to the inner surface of the protractor. The analyzing rod should be located on the mesial or distal sides of the post (Fig. 6).
- Move the device slowly over the surveying platform without changing the cast alignment until the long post of the second implant approaches the analyzing rod. Make sure to keep the facial or lingual surface of the implants parallel to the inner surface of the protractor to ensure making the measurement on the same anteroposterior plane (Fig. 6).
- If the implant to be aligned is mesially inclined, position the cast so that the anterior implants are facing the free movable end of the rotating base. If the implant to be measured is distally inclined, position the cast on the ADD so that the posterior implants are facing the free movable end of the rotating base and the lingual surface of the implants are parallel to the inner surface of the protractor (Fig 6.).
- Rotate the base screw in a clockwise direction to elevate the base rotating in a hinge fashion until the long post on the implant to be aligned becomes parallel to the analyzing rod of the surveyor. Check the angle formed by the base on the protractor. This number represents the angle of the second implant in relation to the reference implant (R) in the mesiodistal direction (Fig. 7).
- The same steps can be followed to measure the angle between both implants in a buccolingual direction. Rotate the cast on the ADD so that the mesial or distal surface of the implants is facing the protractor and make the measurements (Fig. 8).
- If the implant alignment is at a position between the mesiodistal and buccolingual direction (implant is mesiolingually inclined for example), the device can still measure the angle at any direction in 360 degrees around the implant by rotating the ADD device over the surveyor platform and still aligning the impression post parallel to the analyzing rod.
- After measuring all implant angles, attach a straight abutment to the reference implant (R), and choose the corresponding abutment angles for the rest of the implants and screw on the cast to achieve a common path of insertion for the restoration (Fig. 9).
Determining implant inclination in various planes and directions is imperative especially during the prosthetic phase where angulation correction can be achieved by properly selected angled abutments. Conditions can become challenging especially when multiple non-parallel implants need to be splinted in a single restoration. The proposed device can measure the implant angle at any direction and relate it to a reference. Screw or cement retained angled abutments can be selected accordingly.
The advantage of the technique is that it can be used with any implant system to provide an objective estimation of single or multiple implant angulations. The proposed device can measure the implant angle 360 degrees around the implant, not only in 2 dimensions. Screw or cement retained angled abutments can be selected accordingly. The device can also be used to determine the need to prepare prefabricated straight preparable cement retained abutments if the angle between multiple implants is greater than the standard abutment taper. It also provides an easily accessible method that might eliminate the need for an abutment selection kit provided by some implant systems.
The limitations of the present technique involve the need to manufacture the ADD. The measured angle might not be as accurate as digital techniques; however, it is probably enough to give an accurate estimate to the desired abutment angle.
This article describes a simple technique for determining the prosthetic angle of implants. It can also be used to select the proper combination of angles to achieve a common path of insertion for splinted multiunit restorations.
COMPLICANCE WITH ETHICAL STANDARDS
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sector. It was completely self-funded.
CONFLICT OF INTEREST
This is an invitro technique that does not necessitate an ethical approval
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