Bite Splint Therapy: A Review

July 1, 2023
By Lisa Germain, DDS, MScD

Throughout our careers as dentists, patients who present with chronic orofacial pain disorders might be the most complicated treatment dilemmas we encounter.  Each case presents with a unique history, variable comorbid etiologies, as well as perpetuating factors such as stress, parafunction, sleep and airway difficulties, environmental, genetic, and psychosocial influences that contribute to the intensity and persistence of pain. After toothache induced orofacial pain which usually presents as acute, one of the most prominent chronic orofacial disorders we see are the temporomandibular disorders (TMDs). These disorders afflict about 10%–15% of the population at a clinically significant level, with symptoms severe enough to require invasive treatment.  However, a much larger segment of the population is found to have relatively minor signs and symptoms of TMDs (ie.  painless clicking, occasional functional jaw pain, limited or deviated jaw opening). These are not always reported by patients because they do not produce discomfort or often are considered “normal for them”. Recognizing the warning signs of early dysfunction and treating them before they become chronic, and debilitating is crucial; patients with longstanding histories of untreated TMD symptoms often develop chronic pain and usually prove to be quite difficult to treat. [1,2] 

Removable splint therapy in dentistry is a non-invasive treatment modality that has been shown to alleviate the signs and symptoms of TMD.  The intent is to create a harmonious relationship between the muscles of mastication, the TMJ, the articular discs, along with their accompanying ligaments, bones and of course the teeth.  Often these orthotic devices help establish neuromuscular balance in the masticatory system and prevent exacerbation of symptoms through stabilization of the TMJ complex. They also are designed to create a mechanical disadvantage for parafunctional forces. The challenge is determining which kind of splint to use in each individual situation. There are many types of splints.  This article will focus on differentiating some of the most common types, including a discussion on when and where they are indicated.  However, if there is a comorbid sleep disorder diagnosed along with the TMD, how they affect the airway needs to be factored into treatment planning decisions.

SPLINT TAXONOMY

Dawson[3] classified splints as:

  1. Permissive splints/ muscle deprogrammer.
  2. Non-permissive splints/ Directive splints
  3. Pseudo permissive splints (e.g. Soft splints, Hydrostatic splint) 

A permissive splint allows the teeth to move on the splint unimpeded, which in turn allows the condylar head and disk to function anatomically. Examples of permissive splints include bite planes such as anterior midpoint contact splints (anterior jigs, Lucia jig, anterior deprogrammer) and stabilization splints also called full contact splints (flat plane, Shore, Tanner, superior repositioning, and centric relation splint). The anterior midpoint contact permissive splints are designed to disengage all teeth except the incisors thus significantly reducing muscle, clenching, occlusal forces since contact is isolated exclusively in the anterior teeth. This type of splint, inserted during parafunctional movements, is shown to protect the teeth by minimizing wear.  

Bite plane therapy may be used when a muscle disorder initiated by hyperocclusion is suspected.  These splints separate the teeth, allowing the muscles to relax and are mainly recommended in patients with acute or chronic muscle pain.[4]

Stabilization splints are commonly used to treat signs and symptoms of masticatory dysfunction such as muscular and TMJ pain, clicking, crepitus, limited range of motion and incoordination of movement. These work by increasing the vertical dimension thus providing occlusal stability, neuromuscular reprogramming, and condylar self-positioning within the articular fovea. They help to eliminate dysfunctional signs and symptoms of degenerative joint diseases. This type of splint is constructed with even posterior contact in centric relation; the condyles are seated and there is separation of the posterior teeth in protrusive and lateral excursions. It can be used to cover either the maxillary or mandibular dentition. [4]

A nonpermissive splint is designed with a ramp or indentations that position the mandible inferiorly and anteriorly with the intent to secure it there.  Examples of nonpermissive splints are the anterior repositioning appliance (ARA) and the mandibular orthotic repositioning appliance (MORA). These types of splints are also called directive splints and are designed to guide the mandibular condyles away from the fully seated joint position when a painful joint problem is present. Such splints prevent full seating of the joints by guiding the mandible into a forward position on closure into the occlusal splint.[5]

Anterior repositioning splints are used when there is displacement with or without reduction. Displacement with reduction is clinically characterized by reciprocal clicking. The purpose of this splint is to position the mandible anteriorly to maintain the disc in a normal relationship with the condyle. If complete reduction is possible but cannot be maintained, a directive splint is used to position the condyle in the disk to prevent it from slipping back past the posterior band. In cases with severe retrodiscal trauma with edema, a directive splint is used to hold the condyle forward to prevent compression of the retro discal tissues. The patient should be weaned off the splint as soon as the edema resolves to avoid irreversible fibrotic contracture of the superior lateral pterygoid muscle. [6]

Posterior bite plane appliances such as the MORA are designed with a bilateral, hard, acrylic, resin table that is located over the mandibular molars and premolars and connect with a lingual metal bar thus creating disocclusion of the anterior teeth. These appliances are intended to produce vertical dimension and horizontal maxillomandibular relationship changes and need to be followed up with occlusal equilibration to maintain the ideal relationship permanently.  However, the major concern regarding these splints is that occlusion only on posterior teeth for an extended period allows overeruption of the anterior teeth or intrusion of the opposing posterior teeth, eventually leading to a posterior open bite.[7]

Pseudo-permissive splints such as soft splints and hydrostatic splints[8] (Aqualizer TM) function quite differently from permissive splints.  They are used to reduce symptoms of joint dysfunction or myalgia, to prevent bruxism and clenching and as a protective device in athletes. However, these appliances can exacerbate bruxism because their design does not allow for balanced, occlusal contacts.[9]

 

HARD vs SOFT SPLINT 

The most common splints are fabricated from one of two different materials. Hard acrylic resin splints are either self -cured by chemical reaction or heat cured and have a rigid tooth borne occlusal surface. Soft appliances have a flexible tooth-borne occlusal surface. There is a third, hybrid variation which is dual laminated, fabricated with a hard, acrylic, occlusal surface and a tooth borne soft surface.  This construction provides the advantage of a soft splint from the standpoint of comfort and fit and an easily adjustable hard surface. 

Hard acrylic resin occlusal appliances have several advantages over the soft appliances.  The ease of occlusal adjustment, ease of repair, and accurate fit make it a durable choice. The soft splints are more susceptible to wear that in turn result in occlusal changes resulting in a less than ideal occlusal scheme. The soft splints however are a more economical choice.  Various studies have investigated the difference in efficacy of each type as it relates to reduction of bruxism and decrease of muscle hyperactivity.  While some soft occlusal appliances are recommended by some investigators for the reduction of both muscular and arthrogenous TMD symptoms, other studies have shown that they increase bruxism and muscular hyperactivity. [10]

MAXILLARY vs MANDIBULAR SPLINT

When there is partial anodontia, the splint is often made in the jaw where there is the most tooth loss.  The intent is to increase stabilization of the occlusion by utilizing the maximum number of points of contact. If the patient presents with severe incisal overjet, a maxillary arch splint is preferable because it is difficult to achieve proper anterior guidance with a mandibular splint.[11]  When there is a deep curve of Spee or Class III occlusion, a mandibular splint is preferred because it provides a better resting place for the tongue on the anterior palate.[12] It is also reasonable to use a mandibular appliance in a case where a comorbid sleep disorder exists so that the tongue does not block the airway. 

The type of bruxism habit can also dictate whether a splint should be fabricated for the maxilla or the mandible.  A maxillary appliance with all teeth in contact is appropriate for patients who clench isometrically; This is characterized by repetitive tightening and relaxation of the muscles of mastication without mandibular movement.  

A mandibular splint is more effective if the parafunctional movement is created with protrusive movement of the mandible. Patients with lateral parafunction need to have canine guidance created by relieving the contact points on the anterior teeth.  Mandibular appliances are also used for patients who need to wear their splints during the day as well as at night because they do not affect speech as much as a maxillary appliance and are not as visible.  

However, it is preferable for these patients to also have a maxillary splint for use at night to maintain occlusal contacts with equal intensity. [13]

WHICH TYPE OF SPLINT TO USE 

The chart below summarizes which splint is indicated for the most common conditions.  When a patient presents with bruxism and/or headaches, but no joint pain, the use of a full coverage hard acrylic splint is indicated to protect the teeth.  When a muscle disorder such as myalgia, or myofascial pain is diagnosed, bite plane therapy should be used to disarticulate the teeth and allow the muscles to relax. A full coverage stabilization splint with a flat plane surface is recommended.  If muscular pain is present with disc disorder symptoms such as clicking or deviation of the jaw, stabilization splints are recommended and are intended for long term wear. If advanced symptoms of disc and muscle disorders are reported such as locking of the jaw, intense crepitus, and joint pain with limited range of motion, stabilization splints are recommended however must be adjusted to create a balanced occlusion and monitored for relief of symptoms. When a splint is fabricated for cases where there has been acute trauma, and anterior repositioning splint is indicated to keep the condyle away from the inflamed retrodiscal tissues. These appliances should be worn for only 7-10 days while the inflammation subsides.[14]

Summary

Removable dental splints are a useful tool for providing relaxation of the muscles of mastication, helping to seat the mandibular condyle in centric relation, and protecting the teeth from trauma caused by bruxism.  They can also be used for diagnostic purposes and to stabilize an unstable occlusion. Careful evaluation of the patient’s condition should be done to determine which type of splint is indicated.  All splints should be properly adjusted at delivery and readjusted, if necessary, during regular maintenance visits.      

 

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