C-Shaped Molars

Dental practitioners who perform root canal treatment are familiar with the fact that anatomical variations within the radicular structures of the human dentition are abundant.  One especially interesting type of variation that can perplex dentists providing root canal treatment is the C-shaped molar.  This anatomical variant occurs most commonly in mandibular second molars and is present in approximately 8% of the population according to one study. (1)  The prevalence is much higher in specific ethnic groups and was reported at 32% in one study of a Korean population. (2)

C-shaped molars display a wide range of anatomical variation but in general they exhibit a conical shaped root with a deep groove on one side that gives the root the appearance of a letter "C" when viewed in cross section.  The pulp system within the root usually contains a thin band of web-like pulp tissue that may or may not contain distinct canals.  The following cartoon, though over-simplified, is helpful in visualizing the configuration of C-shaped molars in three dimensional space.

                                                                                          

While the cartoon above represents the root canal system as a continuous sheet of pulp tissue, the following diagram (showing cross sections of various types of C-shaped roots) presents a more realistic representation of the variation of canal configurations that can be found.

                                                                          

 From Fan B, Cheung G, Fan M, Guttman J: J Endod 30:899, 2004.

The following micro-CT image shows multiple cross sectional views along the length of a C-shaped molar.  Notice the multiple portals of exit (POE) at the root apex.

                                                                                   

                                                                                                                     rootcanalanatomy.blogspot.com

The complexity of the root canal systems in C-shaped molars increases the difficulty of endodontic treatment.  The dental operating microscope, ultrasonic instruments, agitation of irrigation solutions and 2-appointment endodontics (with inter-appointment placement of calcium hydroxide to penetrate areas that escape direct instrumentation) are all helpful adjuncts that can improve the outcomes of endodontic treatment of C-shaped molars.

The following images display cases of C-shaped molars treated at Mountain View Endodontics. In the image below, webbing between the canals can be appreciated in the coronal aspect of the tooth.  

In the second case (below), webbing can be appreciated in coronal, middle and apical 3rds.

Treatment of the final case (below) was complicated by the presence of a large pulp stone.  The stone was loosened with ultrasonic instruments and the adherent pulp tissue was extirpated almost entirely in tact. 

1. Journal of Endodontics, Volume 24, Issue 5, Pages 372-375, May 1998   2. International Endodontic Journal, Volume 37, Issue 2, pgs. 139-144, February 2004.

Root Amputation

With the proliferation of predictable dental implants over the last two decades, fewer clinical scenarios call for root amputation surgery than in the past.  However, root amputation surgery is still a viable treatment option in certain cases and should be considered when appropriate.

A patient reported to Mountain View Endodontics complaining of significant pain associated with tooth #14. This tooth is the distal abutment for a three-unit FPD.  It  had been treated endodontically by another clinician 6 months previous to evaluation at Mountain View Endodontics.  At the time of the initial endodontic treatment a mostly sub-gingival defect on the DB root was detected when sealer could be seen extruding from the defect on the radiograph.

Radiograph showing defect on DB root marked by extruded sealer

Following completion of RCT, attempts were made by the restorative dentist to seal the defect with restorative material.  These attempts were ultimately unsuccessful as the defect was partially covered by gingiva making proper isolation nearly impossble. Significant gingival recession had occurred on the DB root as well and two attempts at soft tissue grafting to cover the exposed root surface were made but to no avail. Upon exam at Mountain View Endodontics the gingival recession had progressed to the point that the defect became fully visible and the gutta percha used in the initial RCT could be visualized. 

Pre-op intraoral photograph showing defect and gutta percha within DB root

The patient was presented with the treatment options and elected to pursue root amputation surgery.  Due to contamination of the root canal system via exposure to the oral environment through the defect, root canal re-treatment was performed first.

#14 following re-treatment.  Sealer can be seen extruding from defect

#14 following resection of DB root

  

Intraoperative photograph showing resected DB root

Photograph 10 days post-op showing area of resected DB root.

Within two weeks of completion of the procedure the patient was asymptomatic and was pleased to be able to retain #14 and the associated FPD.

Why won't my patient get numb? (Part 2)

In our last post we reviewed a portion of  the Winter 2009 Colleagues for Excellence Newsletter and its discussion of multiple factors that can lead to the failure of our patients to get adequately numb for restorative or endodontic procedures.  In this edition we will review more material from the Newsletter which  focuses on some ways to address failed attempts at anesthesia and also debunks some common myths.
                       
With specific regard to the inferior alveolar nerve block (IANB), it is helpful to keep in mind that while lip numbness usually occurs rather quickly (5-9 minutes), pulpal anesthesia usually requires significantly longer (15-16 minutes).  According to one source (1), in 19-27% of cases, pulpal anesthesia in mandibular teeth takes longer than 15 minutes to achieve after administration of the IANB.  

In light of this information, one important step toward achieving adequate anesthesia is to simply give the anesthetic solution sufficient time to set in.  Additionally, administering the anesthetic slowly (over a period of 60 seconds) rather than quickly (15 seconds) has been shown to be not only less painful for the patient, but also more effective at producing pulpal anesthesia (2).  So when delivering the IANB, remember to slow your roll.                                              
While a second IANB following achievement of lip numbness has not been shown to be helpful, a local infiltration of articaine 4% with epinephrine 1:100,000 following IANB with lidocaine 2% w/ epinephrine 1:100k has been shown to increase pulpal anesthesia.  A 2008 study (3) showed that this method resulted in pulpal anesthesia in mandibular teeth 88% of the time while the success rate was only 71% when the buccal infiltration was done with lidocaine rather than articaine.


Occasionally when lip numbness has been achieved and pulpal anesthesia still eludes us, we as clinicians are tempted to deliver a second cartridge of anesthetic solution via the IANB.  However, studies have shown that if lip numbness is achieved following the first block, adding more solution via a second IANB does not result in better pulpal anesthesia.  The same is true of using an anesthetic formulation with a higher concentration of epinephrine; it does not improve pulpal anesthesia. The perception that a second block results in better pulpal anesthesia is likely the result of the fact that in the time it takes to stop the procedure and administer the second injection, the anesthetic has finally been given sufficient time to fully set in.  Of course, if lip numbness is not achieved after the first attempt, a second cartridge should be delivered.                        

If the patient continues to experience sensation after successful IANB (positive lip sign achieved) and administration of a local infiltration of articaine, an intraligamentary (PDL) or intraosseous injection may be indicated.  While the PDL injection is less successful than the intraosseous injection (3), it is still an excellent adjunct to conventional techniques (IANB and local infiltration) and may be a better option for clinicians unfamiliar with the intraosseous injection technique.  When all else fails, the intrapulpal injection can be utilized for endodontic procedures.  It is particularly effective when back-pressure can be achieved and requires no special syringes or needles. 

Myths:

The Winter 2009 Colleagues for Excellence Newsletter also debunks several myths regarding local anesthesia.  Some of these are listed below.

1.  Contrary to what many of us were taught in dental school, orientation of the bevel (toward or away from the ramus) actually does not affect the success of an IANB (4).

2. Despite popular sentiment to the contrary, studies have consistently failed to show statistically significant superiority of articaine over lidocaine for nerve blocks.

3.  On the question of whether articaine causes paresthesia when used for IANB, conflicting studies have reported different outcomes but the preponderance of the evidence seems to indicate that if articaine is more prone to cause paresthesia, the incidence is extremely low and the authors deem the relationship between use of articaine for IANB and resultant IAN disturbances as "questionable."

4.  Cross innervation does occur in mandibular anterior teeth but it is not the cause of most IANB failures in these teeth.  Rather, these failures are most often due to the anatomy of the IAN bundle (as discussed in the previous blog post).  Therefore, performing an IANB on the contralateral side to the teeth in question is unlikely to produce the desired result (5).

5. "Sticking" or "poking" the soft tissue adjacent to the tooth to be worked on is not a good test to assess the degree of pulpal anesthesia obtained.  Application of a cold cotton pellet to the tooth is a much more useful test of pulpal anesthesia.

    
  
1. Nusstein J, Reader A, Beck M. Anesthetic efficacy of different volumes of lidocaine with epinephrine for inferior alveolar nerve blocks. Gen Dent 2002;50:372-5

2.  Kanaa MD, Meechan JG, Corbett IP, Whitworth JM. Speed of injection influences efficacy of inferior alveolar nerve blocks: A double-blind randomized controlled trial in volunteers. J Endod 2006;32:919-23

3. Haase A, Reader A, Nusstein J, Beck M, Drum M. Comparing anesthetic efficacy of articaine versus lidocaine as a supplemental buccal infiltration of the mandibular first molar after an inferior alveolar nerve block. J Am Dent Assoc 2008;139:1228-35
4. Steinkruger G, Nusstein J, Reader A, Beck M, Weaver J. The significance of needle bevel orientation in achieving a successful inferior alveolar nerve block. J Am Dent Assoc 2006;137:1685-91.
5.  Yonchak T, Reader A, Beck M, Meyers WJ. Anesthetic efficacy of unilateral and bilateral inferior alveolar nerve blocks to determine cross innervation in anterior teeth. Oral Surg Oral Med Oral Pathol Oral Radiol  Endod 2001;92:132-5.

Why won’t my patient get numb?

Occasional difficulty in achieving profound anesthesia for dental procedures is a common experience and one that can be frustrating for both clinicians and patients. What are the factors that occasionally prevent us from achieving anesthesia and how can we improve the frequency with which we successfully get our patients numb? These issues were addressed in the Winter 2009 edition of the biannual clinical newsletter published by the American Association of Endodontists (AAE) entitled Colleagues for Excellence.

The authors of that publication begin by addressing several misconceptions related to the delivery of anesthetic solution via the inferior alveolar nerve block (IANB). One common misunderstanding is the belief that lower lip numbness assures adequate pulpal anesthesia for restorative or endodontic procedures. This is actually not the case. Even after achieving a positive lip sign, adjunctive measures are often needed to achieve pulp anesthesia. Similarly, poking the gingiva or mucosa with an explorer without response from the patient does not assure pulpal anesthesia.

 So does lack of pulpal anesthesia following an IANB indicate that the injection technique was inadequate or that the block was “missed”? In most cases, especially when positive lip sign has been achieved, the answer is no. Studies using ultrasound and radiographs to assure accurate positioning of the needle next to the neurovascular bundles targeted for anesthesia have shown that even with perfect needle placement, pulpal anesthesia is sometimes not achieved. In other words, don’t beat yourself up if your patient doesn’t get numb with a well placed IANB.

 Several factors may contribute to continued sensitivity even following an accurate IANB. According to the authors, the best explanation may be simple anatomy. The inferior alveolar nerve that supplies innervation to all the mandibular teeth on its respective side of the jaw is arranged in layers. As the nerve travels through the mandible, the layers sequentially branch off to supply the molars, followed by the bicuspids, and finally the anterior teeth. This means that at the site of anesthetic delivery, the nerves that supply anterior teeth are in the center or at the core of the nerve bundle and are insulated to some degree from the anesthetic solution. This explanation is consistent with experimental results that show higher IANB failure rates in anterior teeth. 

Several other factors that affect the successful achievement of profound numbness are related to the unique aspects of inflamed tissues. One theory posits that the increased acidity of inflamed tissues inhibits the formation of the base form of the anesthetic solution which is needed to cross the membrane of the nerve cells. The possible effect of this phenomenon when delivering local infiltration anesthesia is clear, however its relationship to IANB failures is unclear since with the IANB the solution is usually delivered at some distance from the focus of inflammation. Additionally, nerves in inflamed tissues have decreased excitability thresholds which can result in the inability of anesthetic solution to prevent impulse transmission in the nerves.

 Another factor contributing to anesthesia failure in areas of inflammation has to do with the types and quantities of ion channels in the membrane of the neuron. Studies have shown that nerve cells in pulps with irreversible pulpitis show a greater expression of sodium channels than nerves in non-inflamed pulps thereby affecting their excitability. And a specific class of sodium channels called Tetrodotoxin-resistant (TTXr) channels has been shown to resist the action of local anesthetics. Lastly, patients in pain are often apprehensive. Though the mechanism is not completely understood, this apprehensiveness has been shown to actually decrease pain thresholds.

So as the preceding points make clear, there are many factors affecting our ability as clinicians to help our patients achieve profound anesthesia prior to restorative or endodontic procedures. In our next post we will address multiple helpful strategies for overcoming inadequate anesthesia as well as debunk some other common misconceptions.

Radiolucencies

For a dental professional who looks at dental radiographs frequently, coming face to face with a radiolucent lesion in the alveolar bone of our patients is an extremely common occurrence. Most often, these lesions are associated with teeth that are in need of endodontic treatment.  In fact, according to a recent article in the Journal of Endodontics,* over 90% of radiolucent lesions associated with teeth are either a cyst, apical granuloma, or an abscess.  Sometimes these lesions are affectionately referred to as LEOs (Lesions of Endodontic Origin). 

While it is clear that most radiolucent jaw lesions are LEOs, the literature is anything but clear on the distribution of the various types.  For example, different studies have reported the incidence of cysts to be anywhere from 6% to 55% and that of granulomas to be anywhere from 46% to 94%.  Such wide ranges make it difficult to predict with any accuracy the exact nature of a radiolucent lesion.  However, does it really matter whether the lesion in question is a cyst, granuloma or abscess?  Historically, this question may have been more pressing because most experts believed that surgical enucleation of cysts was necessary in addition to non-surgical root canal treatment, whereas teeth with associated granulomas could be effectively treated with root canal treatment alone.  

However, recent data suggest that even some cysts can resolve with proper non-surgical root canal treatment utilizing stringent infection control.* But what should be done when the lesion doesn’t heal (i.e. the lesion is still present radiographically with or without accompanying symptoms)?  A non-healing lesion should be followed closely to assure no changes take place over time.  If the lesion remains unchanged and the tooth remains asymptomatic, close follow-up without additional treatment may be justified.    However, it is also important to bear in mind that while they are the most common, LEOs are only one entity in a long list of entities that can cause radiolucent lesions in the jaws.   The aforementioned article in the Journal of Endodontics describes a study which utilized data from the Department of Oral Pathology at the University of Minnesota School of Dentistry. The data in this study came from biopsy samples that were analyzed over a period of 15 years representing a total of 9,723 radiolucent lesions in the jaws.  Lesions that were on the ramus or angle of the mandible were excluded.  

The researchers found a wide variety of diagnoses associated with these lesions.  In fact, 30 distinct entities were identified.In the final analysis, 73% of the biopsy samples analyzed were diagnosed as either a cyst or granuloma.  While this seems to contradict the statement made earlier that over 90% of radiolucencies are LEOs, it is important to remember that these samples were from mostly non-healing lesions.  This would result in fewer LEOs because many LEOs resolve following root canal treatment.                       

So what type of lesions made up the other 27% of biopsy samples?  Keratocystic odontogenic tumors (KOT, formerly known as odondogenic keratocyst or OKC) were the most common, making up 8.8% of the samples. Other lesions occurring in the 1-2% range included Central Giant Cell Lesions (CGCL), ameloblastomas and cemento-osseous dysplasia.  Metastatic lesions were identified in less than  1% of the samples.  As mentioned above, many other types of lesions were identified but most at less than 1%.  In summary, it is important to remember that most radiolucent lesions associated with teeth are of endodontic origin.  

However, many other entities exist and must be considered in the differential diagnosis.  Sensibility testing (percussion, palpation, thermal testing) should be performed on all teeth with associated radiolucent lesions.  An abnormal relationship between pulpal diagnosis and radiographic appearance may help identify an entity as not of endodontic origin (e.g. a vital tooth with a large radiolucency).  Non-healing lesions or lesions which don’t seem consistent with pulpal diagnosis should be followed closely and considered for biopsy.     

*Frequency and Distribution of Radiolucent Jaw Lesions: A Retrospective Analysis of 9,723 Cases.  Journal of Endodontics, Volume 38, Issue 6, Pages 729-732, June 2012.

Root End Surgery

Though it pains us to admit it, we here at Mountain View Endodontics have to concede that Root Canal Treatment is not always 100% successful. While it is difficult to quantify success rates due to significant variations in how “success” is defined, multiple studies over various decades have established that well-performed non-surgical root canal therapy is highly successful. With regard to the small minority of cases that do not achieve long term success, the causes of failure are many and varied. Some causes such as inadequate length or density of the obturation (often indicative of inadequate chemo-mechanical debridement), contamination during treatment due to improper isolation, or crown-down leakage can be effectively addressed via endodontic re-treatment followed by placement of a new, high-quality coronal restoration. 

Certain other causes of failure, or for certain restorative reasons, endodontic microsurgery may be a better choice.Historically, endodontic surgery (aka root end surgery, apicoectomy) has not had success rates comparable to traditional non-surgical root canal therapy. However, in the last decade or so, advances in equipment and technique have resulted in excellent success. The Fall 2010 Edition of the Colleagues for Excellence newsletter (www.aae.org/colleagues) addresses this topic and lists some of the enhancements that have led to increased success rates. Principal among these are the use of the dental operating microscope to identify previously unidentified and untreated canals, fins or isthmuses, the use of specially designed ultrasonic tips that permit accurate and well-centered retro-preps, and advanced bio-ceramic materials such as Mineral Tri-oxide Aggregate (MTA) that provide an excellent and biocompatible root-end seal. The result of these improvements is that endodontic microsurgery, with proper case selection and technique, results in success rates reported in the mid-to- high nineties whereas traditional root-end surgery resulted in success rates closer to 50%. 

The following report illustrates a clinical scenario in which apical surgery was indicated: The patient reported to the general dentist for new crowns on #’s 8 and 9.

The all-porcelain crowns were over-contoured and were in supra-occlusion.  The crown on #9 split vertically and the pieces were re-cemented by the general dentist.  The teeth had been previously treated endodontically, and upon clinical testing, both had palpation and percussion tenderness. The pre-op radiograph revealed that both teeth had fiber posts and root filling material that had been extruded beyond the apex.

An initial attempt was made to treat the case non-surgically. The fiber posts were removed from both teeth as well as the obturation material in #8 via non-surgical root canal re-treatment.  However, attempts to remove the extruded gutta percha from #9 from an orthograde (through the coronal access) approach were unsuccessful.

Via apical surgery, the extruded material on #9 was removed, both root ends were resected and the roots were sealed apically with bioceramic material.

The patient had minimal post-op pain following the procedure and the natural dentition has been retained thereby avoiding the well-known challenges of implants in the esthetic zone.

#8 following restoration with a new fiber post, core and crown

#9 following restoration