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 Table of Contents  
REVIEW ARTICLE
Year : 2014  |  Volume : 6  |  Issue : 2  |  Page : 75-79

Sharonlay - a novel postendodontic restorative design for premolars and single rooted molars: A review


Department of Conservative Dentistry and Endodontics, Krishnadevaraya College of Dental Sciences Bengaluru, Karnataka, India

Date of Web Publication10-Mar-2015

Correspondence Address:
Siddapur Mathada Sharath Chandra
Department of Conservative Dentistry and Endodontics, Krishnadevaraya College of Dental Sciences Bengaluru, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2249-4987.152915

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  Abstract 

Root canal treated teeth are structurally compromised as a result of loss of tooth structure due to caries, iatrogenic cavity preparation, and dehydration. Given that a direct relationship exists between the amount of remaining tooth structure and the ability to resist occlusal forces, it is vital to provide a restoration allowing cuspal coverage as soon as possible following completion of the root canal treatment. A decision to provide a full crown or an onlay depends on the remaining tooth structure, if the cuspal width to length ratio is 1:2 or more, an onlay can be placed. When the ratio is <1:2, a full crown has to be planned. In single rooted teeth requiring postendodontic restoration cast post and core or a prefabricated post can provide resistance to fracture with comparable results. However in case of premolars, where only cuspal coverage is being practiced, it would require cervical reinforcement in addition, to counter the horizontal force acting at the cervical region. A new onlay design with a post extending into the radicular portion of the premolar providing the required reinforcement in a conservative manner and protecting it against both vertical and horizontal forces is proposed herewith called as SHARONLAY I.P. no 1956475.

Keywords: Single rooted premolar, post endodontic restoration, Sharonlay


How to cite this article:
Sharath Chandra SM, Singh R. Sharonlay - a novel postendodontic restorative design for premolars and single rooted molars: A review. J Oral Res Rev 2014;6:75-9

How to cite this URL:
Sharath Chandra SM, Singh R. Sharonlay - a novel postendodontic restorative design for premolars and single rooted molars: A review. J Oral Res Rev [serial online] 2014 [cited 2018 Jan 17];6:75-9. Available from: http://www.jorr.org/text.asp?2014/6/2/75/152915


  Introduction Top


A tooth requires endodontic treatment as a result of caries, trauma or noncarious lesions repeated restorations involving pulp. Many changes occur to a tooth after root canal treatment, including changes in the physical and chemical properties of dentin, its elasticity, resistance to fatigue, changes in the morphology, biomechanical behavior and loss of proprioception. [1] Along with the cause of the root canal therapy resulting in reduced tooth structure, the root canal treatment procedures, that is, access cavity preparation, straight line access to the root apex or up to the initial curvature, shaping of the canal, use of various irrigants including the chelating agents etc., further adds up to the removal of sound tooth structure influencing the fracture resistance of the teeth. [2, 3, 4]

Postendodontic restoration today is considered equally as important as the instrumentation and obturation of the root canal. Prior to the post endodontic restoration, full clinical assessment of the endodontic procedure should be performed. [5]

The restoration must protect the tooth against the load placed on it by distributing the stress throughout the supporting tissues. [6] Studies have clearly shown that oblique loads generate much more intense cervical stress than loads directed along the long-axis of the tooth. [7,8] This is usually seen in single rooted teeth due to nonaxial loading [9] however, the role of the post in providing reinforcement, regardless of the quantity of residual coronal dentin, has been demonstrated. [10]

Ray and Trope [11] evaluated the relationship between the quality of the coronal restoration and the quality of the root canal filling by examining the radiographs of endodontically treated teeth. They observed that a combination of good restorations and good endodontic treatments resulted in absence of periapical inflammation in 91.4% of the teeth, whereas poor restorations and poor endodontic treatments resulted in the absence of periradicular inflammation in only 18.1% of the teeth examined. Furthermore, where poor endodontic treatments were followed by good permanent restorations, which appeared radiographically sealed, the resultant success rate was 67.6%. They concluded that apical periodontal health depended significantly more on the coronal restoration than on the technical quality of the endodontic treatment. [11] The importance of a good restoration to the periapical health was confirmed in similar studies. [12, 13, 14, 15]

Many treatment alternatives for corono-radicular reconstruction for cervical reinforcement of endodontically treated teeth have been studied and have been successfully been used till now like custom cast post and core, prefabricated post with core, fibre post with composite core etc., finally restored with crown/onlay. [16, 17, 18, 19, 20] Previously, Richmond crowns [21] have been documented in the literature as a restoration which provides both occlusal and cervical reinforcement when there is minimal cervical tooth structure and adequate ferrule. [22, 23, 24, 25, 26]


  Onlay Top


Onlay are the mostly indicated and universally used cast restorations for individual teeth. It is partly intracoronal and partly extracoronal type of restoration, which has cuspal protection as the main feature. [27]


  Indications Top


  1. In the cast restoration, cuspal protection is mandatory, if the width of the lesion extends one half of the intercuspal distance.
  2. In tooth preparation, if the length:width ratio of cusp is more than 1:1, but not exceeding 2:1, cuspal protection is to be considered.
  3. In a cast restoration tooth preparation, if the length:width ratio of the cusp is >2:1, cuspal protection is mandated.
In a crown, the restoration margins are at the gingival margin which may effect the gingival health and also supra eruption of the tooth leads to exposure of the gingival margin of the restoration. However, this disadvantage of a crown is overcome in an onlay as the margins are above the height of contour. The preparation in case of an onlay is more conservative as compared to full crown. Hence there is always scope for full crown at a later date especially in growing adolescent patients.

A direct relationship exists between the amount of remaining tooth structure and the ability to resist occlusal forces. [28] Hence, a post endodontic restoration that reinforce the weakened endodontically treated tooth becomes the prime concern of the clinician. [29]

Studies have shown that the greatest stresses are generated at the cervical region of the endodontically treated teeth, [29] especially in single rooted teeth due to angular forces acting on them, due to less surface area for dissipation of forces and because of the position of tooth in the dental arch. Hence, post endodontic restorations should be given keeping in mind the increased survival of endodontically treated tooth in the oral cavity.

The presence of root canal post is thought to reduce the cervical stress, as it acts as a stress distributor, within the radicular dentin when loaded on the core and the prosthetic crown. [30] Post along with main function of retaining the core in severely damaged teeth, also provide reinforcement, even in the presence of sufficient coronal dentin. [31,32] This is in contrast with many studies published previously according to which root canal post do not reinforce the tooth, in fact post space preparation weakens the tooth. [33]

Cast posts are commonly advocated in cases with significant amount of tooth damage and ensure better adaptation of the post to the radicular tooth [34] when compared to a prefabricated post which is useful in teeth with sufficient coronal dentin and fit also depends on the shape of the canal. [35]

A cusp coverage restoration increases the survival and longevity of an endodontically treated tooth. [36] However, partial coverage restorations like onlays not only encompass all the cusps of the treated tooth like a full coverage crown but at the same time is a more conservative approach to the full coverage restorations especially when the tooth structure is intact, therefore conserving lot of sound tooth structure. [37]

Studies have proved that the fracture resistance of endodontically treated teeth was increased when restored with onlay than the average chewing load in the posterior region. [38] Yamada et al. reported that endodontically treated maxillary premolars with mesio-occluso-distal cavities could be successfully restored with cast metallic onlay and inlay. [39]


  Why Special Consideration for Premolars? Top


Premolars are usually bulkier than anterior teeth, but often are single-rooted teeth with relatively small pulp chambers. For these reasons, they require posts more often than molars. Premolars are more likely than molars to be subjected to lateral forces during mastication. The remaining tooth structure and functional demands are, once again, the determining factors. Because of the delicate root morphology present in some premolars, special care must be exercised when preparing a post space. [40]

Keeping these factors in mind, a new onlay with post design, Sharonlay which was thought to have the advantages of both onlay in preservation of coronal tooth structure and post for cervical reinforcement with minimal radicular preparation was introduced.


  Sharonlay (A Patented Design I.P No. 1956475) Top


Definition

It is defined as an onlay with a post extension indicated for endodontically treated single rooted premolar or single rooted molar and also two rooted premolar when one of the canal is parallel to the line of draw [Figure 1] in order enhance the retention of the onlay and also protect the tooth against compressive and tensile forces.
Figure 1: Sharonlay design

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Indications

  1. Indicated in premolars and molars with proximal carious exposure where the cuspal damage is ideal for onlay preparation. Here the post extension enhances the retention of the Onlay, especially when the size of the premolar is small. The post also reinforces the cervical neck of the endodontically treated tooth preventing the horizontal fracture at the neck of the tooth. Hence, Sharonlay counters the compressive and tensile loading on the endodontically treated premolar and single rooted molar teeth.
  2. In the case of subgingival proximal margins as it is difficult to place direct restoration specially resin composites where moisture contamination is difficult to control. Sharonlay being a single unit restoration, has only a tooth restoration interface in subgingival region as compared to multiple interface (tooth, core & crown interface) seen in a core build up with crown in subgingival margins possibility of microleakage reduced to one. The marginal leakage at the tooth restoration interface is further reduced by the placement of bevels. A lapslide joint in the gingival seat created by definite gingival bevel and subsequent marginal wax up during wax pattern preparation can further eliminate the microgap considerably.
  3. When the vertical dimension of the tooth is small and tooth destruction is not extensive.



  Contraindication Top


  1. Not indicated for extensively damaged crown which cannot support an Onlay.
  2. In cases where extensive radicular dentin removal is required to align the post with the Onlay specially in mandibular first premolar where crown is inclined at 30° to the root.



  Advantages Top


  1. Conservation of coronal tooth structure.
  2. Cervical reinforcement of the endodontically treated tooth
  3. Good gingival health - in case of subgingival margins.
  4. Economical
  5. Esthetically better as compared to the full metal crown.
  6. Provides good retention and resistance to the post endodontic restoration.

  Materials of Choice Top


Base metal alloy, gold alloys, indirect composites, ceramic using computer-aided design-computer-aided manufacturing (CAD-CAM).


  Case Selection for Sharonlay Top


In single rooted premolars, it can be fabricated for mesio-occlusal, disto-occlusal or mesio-occluso-distal lesions as a postendodontic restoration. It is also indicated in premolars with two roots where at least one of the roots is parallel to the line of draw planned for the Sharonlay. Also indicated in single rooted molars where additional retention by means of extension into the root canal is required.


  Step by Step Procedure for Sharonlay Top


Completion of root canal treatment



Post space preparation till peeso 3 or 4 depending on the initial diameter of the canal and canal preparation for endodontic treatment



Internal walls of the coronal cavity finished with 5° taper on each wall



Buccal and Lingual cusps reduced 1-2 mm depending on the casting material used (base metal or zirconia)



Counter bevel of. 5 mm on buccal and 1 mm on lingual (for esthetic reason for metal - visibility on buccal side)



Direct or Indirect fabrication of the wax pattern (coronal and radicular portion as one unit) [Figure 2]
Figure 2: Fabrication of Sharonlay (courtesy: Dr. Subhashini)

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Casting of the wax pattern



Trial fit of Sharonlay and final cementation [Figure 3]
Figure 3: Cemented Sharonlay on premolar

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In conventional post and core restorations, the post is extended three to five mm short of the apex, whereas in Sharonlay the radicular extension can be kept as minimal as possible (minimum 7 mm) so as to enhance resistance at the cervical region. Since, the post is used to provide resistance at the neck retention is not a major concern, however, in cases where the coronal tooth structure is weakened the length of the post can be proportionately increased. The diameter of the post would depend upon the final preparation of the canal, with minimal enlargement with size no. 3-4 peeso reamer in order to orient the post to the overlying onlay and provide adequate strength to the post.

The onlay is designed to conserve the tooth structure and preserve any healthy marginal ridge. The design is planned keeping in mind the esthetic requirement and the hooding effect required to prevent splitting of the crown.

Sharonlay being a single unit restoration is generally fabricated in cast metal which is the most economical and durable long term restoration for a single rooted endodontically treated premolar or molar.

A preliminary in vitro study was carried out which compared the fracture resistance of endodontically treated tooth restored using this novel design (Group I) with a two component restoration that is, post with separate onlay (separated by 2 mm) (Group II). Sharonlay showed maximum resistance to fracture with a mean fracture resistance of 514.67N, which is higher than the maximum voluntary bite force recorded in the pre molar region (422 ± 22N in males and 349 ± 24N in females). The fracture lines for both control group (Group III-only onlay without radicular extension) and Group II were seen at the cervical level splitting the cusps while in the Sharonlay group it was seen at the apical extent of the post. These findings indicate that this novel design reinforces the cervical region of premolars. [42]


  Conclusion Top


Premolars are subjected to both tensile and compressive stresses at the cervical region. Clinicians pay minimal attention to cervical reinforcement especially when there is adequate coronal tooth structure. In our in vitro study, the findings indicate that the post gives cervical reinforcement contrary to some of the studies. [13]

Sharonlay design which is a single component (onlay with post) has been tested clinically for more than a decade. Evaluation of these restorations after 10 years shows promising long-term success; however, selection of appropriate case is of prime consideration for the final success of the restoration.

One of the limitations is the visibility of metal on the premolars; alternatively, with the advancement and availability of CAD-CAM technology the same design may be fabricated using zirconia. However the post diameter is critical in this reference. Study regarding post diameter for zirconia Sharonlay is in progress.

 
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  In this article
Abstract
Introduction
Onlay
Indications
Why Special Cons...
Sharonlay (A Pat...
Contraindication
Advantages
Materials of Choice
Case Selection f...
Step by Step Pro...
Conclusion
References
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