And How Do You Harmonize My Bite?

 

           Harmonizing your bite (also known as an occlusal adjustment or equilibration) is a reshaping of the incising and chewing surfaces of your teeth to balance your bite (also called your occlusion) with the position of your jaw joints (technically known as temperomandibular joints or “TMJs”).  This is done selectively, either using a handpiece (dental drill) to reduce areas of interference, like smoothing a rough spot with an emory board, or employing dental materials such as composite (bonding) or crowns (caps) to augment areas needing support.  If your bite and your jaw joints are not in harmony, several negative consequences can result.  Your teeth can become severely worn, your TMJs (as well as the muscles that work with them) can become painfully strained and in extreme cases the cartilage inside your TMJs can become displaced or even torn.  The extent of these problems can be directly related to the degree of disharmony, although some people can adapt remarkably well to significant discrepancies in their occlusion/TMJ relationship and have no complaints.

           Think of your body as your home (it is) and your mouth as the entrance to your home (it also is).  Your occlusion-TMJ system is like the doorway to your home where the hinges are your TMJs and the door/frame interface represents your bite.  In a perfect world, when you close your front door, it  lines up perfectly in its frame with no strain on the hinges in doing so.  If things don’t line up (as when the doorway's wood swells in the summer humidity), however, to close your door you must either twist its hinges so that the door will fit into the frame or you can jam it in into the frame to close it.  If this goes on long enough, either your hinges will start to loosen and then eventually fall apart or your door and frame will wear to the point that you no longer lock your front door.  This kind of imbalance between your bite and your jaw joints can be created by heredity (that may cause a misalignment of your teeth), trauma (such as a fracture of your jaw), tooth loss (with subsequent shifting of your teeth) or a combination of these factors.

 

When this patient's jaw joints are in their most integrated (together)

position, only two of her teeth touch (arrow).  To make all of her teeth

touch in her bite, her jaw joints must dislocate significantly. 

She complained of sore muscles and some of her teeth were excessively worn.

 

           When your bite and your jaw joints aren’t aligned properly, your teeth can wear excessively or become cracked (see the bottom of this page), your TMJs can be injured or some combination of these problems can occur.  This is because your teeth are trying to fit together into the locked position that is your bite, but your chewing muscles (which also control the position of your TMJs) are trying to keep your TMJs in their proper place.  This is a constant battle that can cause tooth wear (when the muscles succeed in keeping the joints in place and the teeth grind each other down as they are pulled out of the bite) or muscle spasm and joint pain (when the bite stays locked as the joints with their associated muscles are stretched to the limit, if not beyond).  The former is why spouses of these patients often note that they grind their teeth in their sleep.  Men tend to exhibit more tooth wear and have less joint pain as their more vigorous chewing muscles tend to keep their TMJs in place.  Women tend to show less tooth wear in these situations while experiencing more joint pain as their more delicate muscles cannot overcome their bites and so their TMJs suffer.

 

           The most desirable way to correct an occlusion/TMJ conflict is to modify your bite, as noted in the emory board example above.  Alteration of your joint is not advisable unless it has been damaged internally when surgery may be needed to repair severely dislocated or torn cartilage.  This repair should only be undertaken after the underlying cause of the injury, the occlusion/TMJ disharmony, has been resolved.  Your jaw joints (like any of your joints) function best when in their most integrated (together) position.  Any dislocation of your TMJs that your bite might cause is detrimental in some way, if sometimes imperceptibly.  This is why it is always better to correct any occlusion/TMJ deviation by placing your TMJs in their most integrated position and then adjusting your bite to match when problems do develop.

 

           There are three ways to revise your bite, realigning it through orthodontics (braces), rearranging your jaw position surgically below your TMJs to similarly improve your bite’s alignment and harmonizing.  Orthodontics or surgical jaw repositioning may be done first if the adjustments that harmonizing would entail are so drastic that too much of your tooth structure would need to be reduced in some areas to be practical or some teeth would need to be built up so much in other areas that they would look unnatural.  Most often, harmonizing is also needed after orthodontics and surgical jaw repositioning, as these are approximate refinements that normally require afterwards the further fine-tuning that harmonizing represents. In some cases the process of harmonizing itself may still necessitate the restoration of one or more of your teeth.  Surgical jaw repositioning is much less commonly used in these circumstances than orthodontics and is thought of as a last option.  

 


 The same patient's centric relation record shows the only point of contact (arrow) in her bite when

her TMJs are in their stable position.

 

           Before any of these steps can be taken, a registration of your bite when your TMJs are in their most integrated position must be taken.  This procedure is called a facebow transfer with a centric relation record and it allows stone models (poured from impressions of your teeth taken at the same time as the facebow transfer) to be mounted on a device called an articulator.  The articulator simulates the movements of your TMJs.  Once the stone models of your upper and lower teeth have been mounted on the articulator according to the facebow transfer and centric relation record, Dr. McArdle can study your bite and determine how your teeth need to be harmonized so that your bite will come together evenly while your TMJs remain stable.  The harmonizing is planned out at this stage by practicing it on the models of your teeth that have been mounted on the articulator and keeping notes of the adjustments needed.  This study is called an occlusal analysis.

 

An articulator, on which stone models of your teeth can be mounted according to a facebow transfer and 

centric relation record, is an instrument that simulates your TMJs with its adjustable hinges (arrows).

 

           Once Dr. McArdle has completed this analysis, you will have another appointment where the harmonizing is actually performed.  Once you have been harmonized so that your TMJs remain integrated while your bite comes together evenly, your chewing muscles will be more comfortable, your teeth will wear significantly less and any restorative treatment you need (such as crowns or bridgework as well as implants) will be more successful without the excessive grinding forces that formerly existed complicating it.  Patients who grind significantly due to discrepancies in their occlusion/TMJ relationship are much more likely to fracture porcelain off of crowns and bridgework or dislodge these restorations.  Implants are also more likely to fail under these forces.  If you have any questions about harmonizing your bite or the conditions that might necessitate it, please ask Dr. McArdle.

 

During orthodontics, with the patient's jaw joints in their most stable, integrated (together) position, a more

even bite develops with many tooth contacts on both sides of her mouth. Afterwards, a study

harmonizing in the laboratory will show how to fine tune her bite.

 

  Post orthodontics a study harmonizing allows the patient's bite to close correctly with the models
on the articulator and its hinges set to her jaw joints' most stable, integrated (together) position.

This result was duplicated in the patient's mouth before restorative treatment started.

 

This is what the patient's actual bite looked like at her front teeth prior to being harmonized...

 

...and this is how her bite looked at her front teeth after being harmonized.

 

This is how the patient looked after her harmonized smile was definitively restored.

 

IF YOU ARE CONSIDERING EXTENSIVE ESTHETIC DENTAL TREATMENT, REQUIRE COMPLETE FUNCTIONAL

DENTAL TREATMENT OR A COMBINATION OF BOTH IS CALLED FOR, VERIFYING THE STABILITY OF YOUR

BITE AND HARMONIZING IT IF NEEDED IS A NECESSARY FIRST STEP!

 

 

 

 

 

J Prosthet Dent. 2001 Aug;86(2):168-72.


Type and incidence of cracks in posterior teeth.

Ratcliff S, Becker IM, Quinn L.

Visiting Faculty, The Pankey Institute, Key Biscayne, Fla., USA. Houzbayou@ameritech.net

STATEMENT OF PROBLEM: The use of magnified vision in the operatory has enhanced the early diagnosis of structural defects in the dentition and in existing restorations. There is little in the literature to guide the clinician on the significance of cracks and other interruptions in the integrity of teeth. PURPOSE: This study characterized the type and incidence of cracks in posterior teeth and identified possible etiologic factors. MATERIAL AND METHODS: An observational cross-sectional survey of 51 patients from a private practice examined during an 18-month period was used to identify 4 types of cracks in posterior teeth. The study identified both patient- and tooth-level variables present in each patient examined. The data were subjected to statistical analysis to determine whether correlations existed between the variables and cracks. RESULTS: Cracks in teeth were shown to have chronicity and can be classified according to appearance. Variables such as the presence of a Class I or II restoration and the presence of excursive interferences were shown to significantly increase (P< .0001) the chances of a crack being present. Combinations of variables, such as interferences and a restoration, also increased the chance of a crack being present. CONCLUSION: Within the limitations of this study, the presence of cracks in teeth was associated with the placement of a Class I or II restoration and with the presence of excursive interferences. Age played a role in the presence of stained or symptomatic cracks, which suggests that cracks have chronicity. Although many questions remain regarding prevention, it is evident that protecting teeth from excursive interferences and parafunction may thwart premature breakdown.

 

The Journal of the American Dental Association
 
 
 
 
 
 

Risk Indicators for Posterior Tooth Fracture
James D. Bader[1], Daniel A. Shugars[2], Jean A. Martin[3]
JADA 2004; 135:883-892.

Abstract

Background. Identifying posterior teeth that are at heightened risk of developing cusp fracture is an inexact science. Risk indicators based on controlled observations are not available, and dentists' assessments vary. Methods. The authors conducted a case-control study of cusp fracture in restored posterior teeth. They evaluated 39 potential risk indicators identified in previous uncontrolled studies for an association with fracture in 200 patients with fractures and 252 patients without fractures. These risk indicators delineated patients' clinical characteristics and behaviors, as well as clinical characteristics of individual teeth. The authors used logistic regression to develop models identifying risk indicators associated with fracture, both between case and control subjects and between case and comparison teeth in case subjects. Results. Two risk indicators appeared in both models. The presence of a fracture line and an increase in the proportion of the volume of the natural tooth crown occupied by the restoration substantially increased the odds of fracture (P < .001). Additional risk indicators were unique to the case subject–control subject model, including subject age and other measures related to the relative size of the restoration or to loss of dentinal support. Neither patient behaviors such as clenching, grinding and biting hard objects nor occlusal characteristics such as guidance, cusp anatomy and general wear patterns were strong predictors of fracture risk. Conclusions. Among posterior teeth with restorations, two clinical features were strongly associated with the risk of cusp fracture: presence of a fracture line in the enamel and proportional volume of the restoration. Clinical Implications. Dentists assessing the risk of fracture should consider a detectable fracture line or a high ratio of restoration-to-total-crown volume as important indicators of elevated fracture risk.




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Dr. Barry F. McArdle, D.M.D. ~ 118 Maplewood Avenue, The Captain Moses House, Suite B-7, Portsmouth, NH 03801

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