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Year : 2023  |  Volume : 14  |  Issue : 1  |  Page : 48-51

Enamel island technique and nonrigid connectors: A viable rehabilitation protocol

1 Command Military Dental Centre, Udhampur, Jammu and Kashmir, India
2 Department of Prosthodontics and Crown and Bridge, Command Military Dental Centre, Udhampur, Jammu and Kashmir, India

Date of Submission08-Jul-2022
Date of Decision25-Nov-2022
Date of Acceptance28-Dec-2022
Date of Web Publication18-Mar-2023

Correspondence Address:
Dr. Poonam Prakash
Prosthodontics and Crown and Bridge, Command Military Dental Centre, Udhampur - 182 101, Jammu and Kashmir
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/srmjrds.srmjrds_92_22

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Rationale: Fixed denture prosthodontics is a commonly practiced treatment option for rehabilitation of partially edentulous clinical conditions. Certain local and systemic factors contraindicate utilization of implant therapy. Long edentulous span, pier abutment, distal abutments, and intersegment prosthesis extending from one sextant to another are a few challenging situations due to altered biomechanics and require modification in treatment planning to achieve optimum outcome. Patient Concerns: A 37-year-old male patient reported with difficulty in mastication due to partially edentulous mandibular arch. Diagnosis: Based on clinical features, a diagnosis of Class II partially edentulous mandibular arch was made. Intervention: Rehabilitation of partially edentulous mandibular arch was done using customized semiprecision attachment. Outcomes: Recall appointments were scheduled at 48 h, 1 week, 1 month, and 3 months and the patient was found to be satisfied with the prosthesis. Lessons: Semiprecision attachment is a viable modality that is used in rehabilitation of pier abutment situations. It protects the abutment from unwanted leverage forces and ensures longevity of the restoration.

Keywords: Abutment, attachment, enamel island technique, partially edentulous

How to cite this article:
Bahri MR, Prakash P. Enamel island technique and nonrigid connectors: A viable rehabilitation protocol. SRM J Res Dent Sci 2023;14:48-51

How to cite this URL:
Bahri MR, Prakash P. Enamel island technique and nonrigid connectors: A viable rehabilitation protocol. SRM J Res Dent Sci [serial online] 2023 [cited 2023 Mar 20];14:48-51. Available from:

  Introduction Top

Fixed dental prostheses for the rehabilitation of missing dentition are the gold standard in field of prosthodontics. Primary requisite for a successful prosthesis is axially and well distributed occlusal loads which can be achieved with healthy abutments, strong connectors and properly planned pontics. To achieve the desired load distribution, distal terminal stop is required and accurate interocclusal records are needed to transfer the same relation on an articulator. This ensures complete occlusal harmony in centric and eccentric contacts.

Challenge arises when the posterior vertical stop is either missing or the last available tooth becomes the terminal abutment of the prosthesis. This makes orientation of the cast in correct occlusal relation difficult. Another method that has been advocated in literature is preservation of centric stop or the island technique.[1]

Glossary of Prosthodontic Terms defines Pier abutment as “A natural tooth or implant abutment that is located between terminal abutments that serve to support a fixed or removable dental prosthesis.”[2] Biomechanics of occlusal load in these situations change and due to lever action, the stress concentration on the pier abutment is increased. Due to arch position, physiological tooth movement, and retentive capacity of retainers, the treatment plan requires modification.[3] Use of nonrigid connectors like tenon-mortise, split pontic or crosspin and wing are recommended in such situations. The most common design is the key-keyway where a female component is designed at the distal end of the pier and the male component is attached to the pontic distal to it.

This clinical report highlights the rehabilitation of a patient with partially edentulous mandibular arch presented with distal abutment and a pier abutment. This case showcases the fabrication of custom-made semiprecision attachment instead of prefabricated patterns. Furthermore, the case presents an alternative to conventional interocclusal record by modification of tooth preparation technique utilizing enamel island technique.

  Case Report Top

A 37-year-old male patient reported to a tertiary care dental center at Udhampur with a chief complaint of difficulty in mastication and altered esthetics due to missing teeth in lower back tooth region for 4 years. History revealed extraction of mandibular first premolar and first molar on the right side 4 years back secondary to caries and endodontic treatment in the mandibular second premolar. Intraoral examination revealed missing 44, 46. 45 was endodontically treated with sound periodontal health. All the maxillary and mandibular third molars were missing. Examination of edentulous site revealed compromised bone width of bone in 44 with a bone defect on buccal aspect. Based on clinical features, a diagnosis of Prosthodontic Diagnostic Index Class II partially edentulous mandibular arch was made [Figure 1]. Treatment options explored were Implant retained prostheses in 44,46 with full coverage PFM restoration wrt 45, fixed dental prosthesis from 43-47 or a removable prosthesis.
Figure 1: Pretreatment view (a) Extraoral; (b and c) Intraoral

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Treatment options were discussed with the patient, and the 2nd option of fabrication of 5 unit Fixed dental prosthesis (FDP) was chosen and an informed consent was obtained. The components planned were a custom-fabricated key-keyway type of nonrigid connector in the region distal to second premolar with full coverage porcelain fused to metal retainers in 43.45 and 47, modified ridge lap pontic in 44, and sanitary pontic in 46.

Since 48 was missing and distal abutment was 47, enamel island technique was followed to allow proper orientation of cast. Diagnostic impressions were made using irreversible hydrocolloid impression material (Zelgan 2002, Dentsply, India) and orientation relation was recorded using UTS 200 facebow. Centric relation records were made and the cast was mounted on Stratos 200 semiadjustable articulator. Diagnostic wax-up was done to estimate the amount of tooth preparation required and also to serve as an index for fabrication of provisional restorations.

Enamel island technique

To identify the cusp to be used as an island, articulating paper of 80u thickness (Bausch, United States) was used. Maximum intercuspal position was recorded and the cusp with darkest mark, i.e., distobuccal cusp, was delineated as the stop [Figure 2]a. Tooth preparation was done following biomechanical principles of tooth preparation. For preserving the centric stop, occlusal reduction of 2 mm on functional cusp and 1.5 mm on nonfunctional cusp was done.[4] However, the distobuccal cusp was not reduced. 43 and 45 were prepared with adequate occlusal clearance, shoulder margin on buccal aspect, and chamfer margin on lingual aspect.
Figure 2: (a and b) Enamel island technique; (c) Preparation of keyway

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Non rigid connector

The area on disto-occlusal surface of the second premolar was prepared creating a keyway about 1.5 mm deep with rounded internal line angles. The extension of keyway was one-half of buccolingual dimension and one-third of mesiodistal dimension with occlusally divergent walls[5] [Figure 2]b and [Figure 2]c. Final impression was made using two-stage putty wash technique (Affinis, Coltene, Switzerland) and the cast was mounted using facebow and centric relation record on a semiadjustable articulator. After mounting, the centric stop was in contact with opposing tooth. Once the models were mounted, the centric stop island was carefully trimmed on the articulated models. This allowed us to achieve adequate clearance for fabrication of provisional restorations following indirect method. Prior to luting of the provisional restoration, the centric cusp stop was removed intraorally and provisional restorations were luted. For definitive restoration with nonrigid connector, wax pattern was fabricated using type II inlay wax. Complete anatomic wax-up was done and a cutback was provided to ensure uniform clearance for application of porcelain. Jelenko surveyor was used to carve the wax pattern on disto-occlusal surface of the second premolar to create a keyway with parallel walls to ensure smooth path of insertion for the male counterpart on pontic distal to it [Figure 3]a. Once this keyway was prepared, it was lubricated using petroleum jelly and the extension from pontic in the region of mandibular first molar was made toward the keyway [Figure 3]b. [Figure 3]c and [Figure 3]d depicts the wax pattern with key-keyway attachment. The pattern was removed to check for easy and passive removal. The whole assembly was cast using lost wax technique. Coping trial was done to check fit of margins and path of insertion of the custom-fabricated semiprecision attachment. Ceramic (Ceramco3, Dentsply, India) application was done in layers as per the manufacturer's recommendations and staining was done to match patient's adjacent teeth [Figure 4]. The prosthesis was luted using Glass ionomer cement (GIC) type II luting agent and checked for any occlusal interferences using articulator paper [Figure 5]. Mutually protected, canine guide occlusion was achieved. The patient was satisfied with the prosthesis and was given instructions in form of maintenance of oral hygiene. Recall appointments were scheduled at 48 h, 1 week, 1 month, and 3 months.
Figure 3: Fabrication of sectional wax pattern with key-keyway: (a) achieving Parallelism of walls using surveyor, (b) keyway in wax pattern, (c and d) wax pattern with key-keyway attachment

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Figure 4: Definitive prosthesis: (a) Mounting on semiadjustable articulator (stratos 200), (b-d) finished prosthesis

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Figure 5: Definitive prosthesis in-situ: (a) anterior section in-situ with keyway, (b) Anterior and Posterior section in-situ, (c,d) Definitive prosthesis in lateral and frontal view

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  Discussion Top

Enamel island technique was introduced by Christensen with the aim of providing a method of preservation of centric stop. Over the years, many modifications have been attempted such as composite island technique.[6] Other common methods for the preservation of centric stop are a bite record with an appropriate interocclusal materials such as reinforced waxes, elastomeric consistency of recording materials, and others.[7] However, the minimum thickness of dimensionally stable and accurate interocclusal record is variable. The absence of any interpositional material between the occluding surfaces of teeth makes it more accurate. Care should be taken that the portion of enamel left as island should be easily removed on the working cast without altering the tooth preparation. The tooth preparation needs to ensure adequate occlusal clearance at all sites other than point of centric stop.

Attachments are routinely used in prosthodontics for removable and fixed restorations. Semiprecision attachments are available in the form of plastic, resin, or wax patterns which can be incorporated within the wax pattern and cast with the prosthesis. Management of pier abutment conditions requires a nonrigid connector. If a fixed long span prosthesis is planned in such conditions, it acts as a Class I lever and the premolar acts as a fulcrum. This may cause intrusion of the premolar and extrusive pull on the weakest abutment anteriorly or posteriorly.[8] This may result in dislodgement of retainer, loss of retention, debonding, marginal leakage, and eventually secondary caries. Stress breaker allows transfer of load to the supporting bone, minimizes mesiodistal torquing, and exerts less stress on the abutments. Various authors have proposed different positions for the matrix and patrix portion of nonrigid attachment.[9] Oruc et al. conducted finite elemental analysis study and concluded that use of nonrigid connector distal to second premolar reduces stress concentration extensively.[10] Fabrication of customized attachment requires use of surveyor to ensure parallelism of wax pattern and the prosthesis. Recent advances include use of computer-aided design-Computer-aided manufacturing technology for designing and milling of prosthesis which allows complete digital workflow thereby saving laboratory steps and hence time. Although with advancements, the choice of material and technique has changed, the basic principles and concept for management of such conditions remain conventional.

The strength of this approach was that use of enamel island made the procedure more predictable by avoiding the errors that might have occurred using an additional interocclusal recording material. This saved on chairside time of adjustment and ensured proper seating of the prosthesis. The use of customized semiprecision attachment allowed preserving the pier abutment and avoiding development of unwanted stresses on the pier abutment, ensuring longevity of treatment and success of prosthesis. The limitations, however, were that the procedure for fabrication of customized attachment is technique sensitive and requires a certain degree of laboratory skills.

  Conclusion Top

Enamel island technique is a viable, clinically simplified, and accurate method for the preservation of centric stop and precise articulation of casts on articulator. Long span prosthesis extending from anterior segment to posterior segment requires a stress breaker for even dissipation of force and transfer of load to supporting bone. Micromovement between two components of semiprecision attachment reduces the torque, thereby preserving the remaining teeth and ensures the longevity of prosthesis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Sonune S, Dange S, Khalikar A. An accurate interocclusal record by creating a vertical stop. J Indian Prosthodont Soc 2005;5:119-21.  Back to cited text no. 1
  [Full text]  
Ferro KJ, Morgano SM, Driscoll CF, Freilich MA, Guckes AD, Knoernschild KL, et al. The glossary of prosthodontic terms: Ninth edition. J Prosthet Dent 2017;117;e1-105.  Back to cited text no. 2
Yaqoob A, Rasheed N, Ashraf J, Yaqub G. Nonrigid Semi-precision connectors for FPD. Dent Med Res 2014;2:12-21.  Back to cited text no. 3
Rosenstiel SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics, 5th edition, Elsevier, St. Louis, Missouri, 2016.  Back to cited text no. 4
Phoenix RD, Cagna DR, DeFreest CF. Stewart's clinical removable partial prosthodontics, 4th edition, Quintessence Pub, Hanover Park, IL, 2003.  Back to cited text no. 5
Sato Y, Hosokawa R, Tsuga K, Kubo T. Creating a vertical stop for interocclusal records. J Prosthet Dent 2000;83:582-5.  Back to cited text no. 6
Thanabalan N, Amin K, Butt K, Bourne G. Interocclusal records in fixed prosthodontics. Prim Dent J 2019;8:40-7.  Back to cited text no. 7
Caputo AA, Standlee JP. Biomechanics in clinical dentistry, Quintessence Publishing Co, Chicago; 1987. p. 126-37.  Back to cited text no. 8
Adams JD. Planning posterior bridges. J Am Dent Assoc 1956;53:647-54.  Back to cited text no. 9
Oruc S, Eraslan O, Tukay HA, Atay A. Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 2008;99:185-92.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]


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