Introduction To Muscle Strength
By Dr. Jim Prittinen
When treating orthodontic patients, it is critical to always remember the most important principle of orthodontic treatment. That is, the same brackets, bands, and wires may and probably will produce different treatment responses in different patients. Most of these differing responses occur in the vertical dimension. Throughout this book, I will continually emphasize the importance of vertical control in orthodontic treatment. In fact, controlling the vertical dimension is the most important aspect of orthodontic treatment.
This leads us to the next most important principle of orthodontic treatment, which is the worst mistake that can be made when treating an orthodontic patient is to allow the bite to open in a patient who already has open bite tendencies. The reason this is so important is that no matter the severity of the open bite (and whether it is dental or skeletal), it is typically corrected (unless orthognathic surgery is done) with purely dental movement. Indiscriminate bite opening can lead to aesthetic problems such as excess gingival display, excessive down and back mandibular rotation (which, because the mandible opens on an arc, can result in a retrognathic, class II appearance), and, as a result, poor facial aesthetics. Dr. Sassouni's studies (more on that later) pointed out that the poorest aesthetic results occur in patients with long faces. Since this can be a very poor outcome, we obviously want to avoid this. One of the best ways to avoid it is not to treat open bite patients. Bjork stated in his studies (again, more on that later) that approximately 15% of patients have weak muscled, open bite tendencies. So this is a big part of the 25% of cases that the typical general dentist should avoid.
Diagnosis Of Patients With Open Bite Tendencies
As you will see, there are two general categories of mandibular growth direction.
The first category of growth direction occurs in a patient whose mandible rotates upward and forward with growth (the right photo in the above slide). Other terms that are used interchangeably to describe this growth direction are horizontal growth pattern, counterclockwise growth pattern, or (for reasons that will become apparent later) strong muscled patients. The second category of growth direction occurs in a patient whose mandible rotates downward and backward with growth (the left photo in the slide above). Other terms that are used interchangeably to describe this growth direction are vertical growth pattern, clockwise growth pattern, or (for reasons that will become apparent later) weak muscled patients. Every decision that is made during orthodontic treatment will be influenced by this growth pattern and the patient's muscle strength.
Here is another important concept: very few patients are purely forward or purely backward rotators. In fact, most people exhibit some forward and some backward rotating characteristics. But the most difficult cases to treat are patients who exhibit extreme forward and especially extreme backward growth rotation. If these extreme growth patterns can be identified before beginning treatment, the clinician can assess the difficulty of a particular case. It is vitally important to be able to recognize these extreme growth patterns before beginning treatment.
Diagnosis Of Extreme Growth Patterns
Many orthodontic researchers have done studies which have contributed to the body of knowledge that can be used to diagnose a patient's growth pattern. Let's start by discussing Dr. Sassouni's contribution. Before Dr. Sassouni published his landmark growth studies in the mid 1960’s, good orthodontics was defined as the ability to produce "pretty plaster models".
In other words, occlusion was deemed far more important than facial balance. Dr. Sassouni challenged this traditional view by emphasizing the importance of facial balance. He studied cephalometric x-rays and superimposed soft tissue outlines on these x-rays. By doing this, he was able to identify soft tissue characteristics which reflected skeletal variations. This caused Dr. Sassouni to question of aesthetic values of different facial types. To help discover which facial types were considered aesthetically acceptable and which were considered aesthetically unacceptable, Sassouni constructed a series of shadow profiles; examples of which are shown below.
Sassouni showed these profiles to thousands of people-including lay people as well as dental professionals. He asked these people to comment on the aesthetics of these profiles. The most consistent result in this study was that people disliked the open bite profiles. No matter what other profile characteristics a particular patient had, long faced (open bite) profiles were consistently deemed the most aesthetically unappealing profile by a great majority of the lay and dental professional evaluators.
Keep this study in mind but let's now move ahead about 25 years to a study done by Dr. James McNamara, who is on the orthodontic faculty at the University of Michigan. McNamara has always been interested in the mechanics of Class II correction. But, to effectively and efficiently correct Class II problems, it is important to understand the components of a typical class II malocclusion. In 1990, he did a study in which he tried to identify the components of Class II occlusions. The results of the study showed that almost 90% of class II patients (this was measured by using the mandibular plane angle as well as lower anterior face height) had either ideal or long lower anterior face height. He concluded that vertical control was an important aspect of Class II correction.
By combining these studies, we now know that the most unattractive facial profiles are long face profiles. We also know that most class II malocclusions have vertical dimensions that are either ideal or vertically excessive. Therefore, control in the vertical dimension is vitally important in orthodontic treatment.
The Importance Of Vertical Control
This brings us to what I believe is the most important study ever done regarding orthodontic diagnosis and treatment. It was done by Prof. Arnie Bjork. After practicing orthodontics for 25 years, Prof. Bjork accepted the post of Chairman of the orthodontic department at a Danish University. Once he accepted this position, he never again treated another case but instead focused on this study. This study has become one of the landmark studies regarding facial growth and development.
In this study, Prof. Bjork monitored the growth of 248 children. No treatment was performed on these patients. He took records on these kids every year, but what makes this study so valuable is that he also placed metallic implants in the maxillas and mandibles of these growing children. These implants provided a reliable method of superimposition of the cephalometric x-rays. The main reason that this study is so valuable is that it can never be duplicated because of ethical concerns. Prof. Bjork observed some pretty severe malocclusions as they worsened. In today's environment not treating these cases is unethical because of the harm done to the patient by not treating. Additionally, placing implants in children for observation only would today be unethical, whereas it was not considered unethical in the 1950s when Prof. Bjork performed the study. Note: it is interesting to observe the “crude” technique of implant placement. How will today’s “modern” techniques be viewed 50 years from now?
What did Prof. Bjork conclude from this study? First he postulated that the condyle is the driving force behind craniofacial development and that condylar growth direction depends upon the position of the growth cells which are located on the head of the condyle. This, he felt, is an inherited trait so the amount of mandibular growth is genetically determined. But, how this growth is expressed can be influenced by the control of the vertical dimension of occlusion.
Prof. Bjork stated that if the growth cells are located on the anterior surface of the head of the condyle the mandible will rotate in a forward or counterclockwise direction as growth occurs. Conversely if the growth cells are located on the posterior surface of the head of the condyle, the mandible will rotate in a downward or clockwise direction.
Because of muscle size and the angle at which the muscles work differ in these two growth patterns, the forces of mastication are very different based upon growth rotation. In fact, the forces of occlusion can be up to six times more powerful in forward rotating patients than in backward rotating patients. Because of this, forward rotating patients can be characterized as strong muscled patients and backward rotating patients can be characterized as weak muscled patients. The picture below describes how the muscles work based on angles; it also shows that forward rotating patients have muscles that are stronger because they work in a more efficient direction.
Prof. Bjork also postulated that the location of growth cells can be anywhere on the condylar head, so most patients have some forward and some backward rotation characteristics. For our purposes, it is important to understand that the most difficult orthodontic cases are those patients that show extreme forward rotation (these would be very deep bite patients) and especially extreme down and back rotation (these would be open bite patients). Because the muscles of mastication exert pressure and tension in different areas of the mandible depending on condylar growth direction, the shape or morphology of the mandible differs based upon growth direction. In other words, resorption and apposition of bone and therefore morphology of the mandible differs based upon growth direction. This provides the basis for what Bjork called the structural basis of determining mandibular growth direction. Therefore, growth direction can be predicted based upon mandibular morphology; this can be a very valuable diagnostic tool.
As general dentist practicing orthodontics, it is good to know which cases are going to be the most difficult, so we know what cases are candidates for referral. The structural method of determining growth direction enables us to pick out the most difficult cases because the most extreme forward and downward rotators have more distinctive mandibular morphological characteristics than do patients with more average growth rotation. So, this method identifies the extremes in growth rotation; this can be the basis for deciding whether the case should be referred.
One of the most important aspects of orthodontic diagnosis is to recognize specific structural features that develop as a result of remodeling depending upon the direction of mandibular growth rotation. The rotation pattern can affect treatment. Most orthodontic mechanics are extrusive. Patients with a forward rotating growth pattern (these patients can be referred to as strong muscled patients) have masticatory muscles that can easily resist the extrusive component of most orthodontic mechanics. On the other hand, patients with a down and back rotational growth pattern (these patients can be referred to as a weak muscled patients) are often susceptible to the extrusive component of orthodontic mechanics, because their muscles of mastication cannot overpower the extrusive component of the orthodontic mechanics. Since these weak muscled patients usually already have long faces, this extrusion can be very harmful from an aesthetic and functional standpoint. Remember, Sassouni’s studies show that long faces are undesirable from an aesthetic standpoint.
Extreme forward and extreme backward rotating patients are the most difficult cases to treat. Extreme forward rotators have very strong musculature combined with deep bites; it becomes extremely difficult to overpower the muscle strength to open those bites. Extreme down and back rotators present a different set of challenges. They already have open bite tendencies and because of the weak musculature it is very easy to induce additional bite opening. The structural method of diagnosis allows us to predict the difficulty of managing the vertical dimension based upon the shape of the mandible as viewed on the cephalometric x-ray. This is very valuable diagnostic information.
Always remember the most important principle of orthodontic mechanics. That is, the same brackets, bands and wires will produce different treatment responses in different patients. These different treatment responses are expressed as vertical dimension changes. The patient's muscle strength determines treatment response. Finally, the worst mistake that can be made in orthodontic treatment is to cause bite opening the patient who already exhibits open bite characteristics. By not treating open bite cases, you can never make this mistake. If you decide to treat open bite patients, specific mechanics must be done to help limit the vertical dimension increases.
So what are the morphological characteristics that can be viewed on cephs to help determine the patient's muscle strength? The photograph below shows differing mandibular morphologies.
Here are some of the specific morphological changes that can be used to help make a diagnosis of strong or weak musculature.
The first morphologic characteristic that differs in strong and weak muscled patients is the gonial angle. Strong muscled patients have an acute gonial angle, while weak muscled patients have a gonial angle that is more obtuse. Look at the following slide and note the difference in the gonial angle.
Another characteristic that differs in strong and weak muscled patients is the shape of the lower border of the mandible. Strong muscled patients exhibit a double curvature that resembles a reverse S, whereas weak muscled patients present with a concave lower border.
Symphyseal inclination is another characteristic that can be used to differentiate between strong and weak muscled patients. Strong muscled patients tend to have larger chin buttons than do their weak muscled counterparts. This results in a symphyseal inclination that is acute in strong muscled patients, but more obtuse in weak muscled patients.
Symphyseal radio-opacity or radio-lucency is another distinguishing characteristic. Strong muscled patients tend to have thicker bone, and therefore a more radiopaque appearance, in the symphyseal area. Weak muscled patients are exactly the opposite-their symphyseal area tends to be more radiolucent.
Finally, although it may be difficult to see on a cephalometric x-ray, the inclination of the condyle differs in strong and weak muscled patients. Because the growth cells are located more in the anterior surface of the head of the condyle in strong muscled patients, condylar inclination will be more in an anterior direction. Conversely, because the growth cells are located predominantly on the posterior surface of the head of the condyle on weak muscled patients, condylar inclination will be in a more posterior direction. With the advent of 3D imaging, this characteristic is more observable compared to when viewed on a two dimensional x-ray.
By looking for these characteristics, muscle strength and therefore direction of growth rotation can be predicted. This knowledge (as you'll see later) is vitally important in orthodontic diagnosis.
In summary, patients who exhibit extreme forward or extreme backward rotation have very distinct and different mandibular morphologies. Using mandibular morphology is an excellent diagnostic tool which enables the clinician to pick out the extreme forward and backward rotators. Patients will exhibit extremes in mandibular rotation are the most difficult cases to treat. In extreme forward rotators, the resulting deep bites are often difficult to correct because it is very difficult to overpower the strong muscles of mastication. In extreme backroom rotators exactly the opposite occurs. Open bites are very easily induced. Therefore the same orthodontic mechanics used in strong and weak muscled patients will produce vastly different results in the vertical dimension. This is the most important example of the number one rule in orthodontics-that is the same brackets, bands, and wires may and probably will produce different treatment responses in different patients.
An Orthodontic History Lesson
To further understand some of the basics of orthodontic diagnosis, it is important to understand some of the history of orthodontics. Edward Angle is considered the father of modern orthodontics. He practiced around the turn-of-the-century and was an avowed non-extractionist. His rationale for treating all cases non-extraction was "God made the teeth, God made the bones, therefore they fit". Many of Angle’s students, particularly Dr. Charles Tweed, challenged Angle's insistence on non-extraction in all cases. This shows that the extraction/non-extraction debate is not new. Tweed felt that the best way to ensure long-term stability and facial balance in orthodontic cases was to position the mandibular incisors in an upright position. This required extractions in most cases. Because of Tweed's influence, for most of the 20th century, extraction orthodontics dominated the scene. However, many studies have shown that the long-term stability of both extraction and non-extraction cases are approximately the same. In other words, relapse is just as likely to occur in extraction and non-extraction cases. Furthermore, society's views on what constitutes a balanced face and pleasing profile has changed dramatically over the years. The slide below illustrates how "ideal" facial balance has changed.
Because the concept of the ideal face has changed, non-extraction orthodontics (in other words, positioning the anterior teeth more anteriorly so a full profile is the result) is now much more accepted than it was in the middle and late 20th century.
Despite the fact that the Tweed orthodontic philosophy is not as accepted as it once was, many of the studies carried out by Tweed (and, after his death, his foundation) provide valuable insight into orthodontic diagnosis. One particular study by the Tweed foundation compared successful and unsuccessful class II treatment. This study retrospectively looked at both successful and unsuccessful class II correction cases. The differences in treatment response in successful and unsuccessful cases is significant. In successful cases, results consistently showed forward mandibular rotation and lack of molar eruption.
Conversely, unsuccessful cases exhibited down and back mandibular rotation and significant molar eruption.
In summary, successful cases exhibited minimal backward mandibular rotation while unsuccessful cases exhibited extreme backward mandibular rotation. Although this study showed response to treatment, the mandibular rotation that occurred is very similar to the mandibular growth direction as described by Bjork. Successful cases look a lot like Bjork's strong muscled (forward rotating) patients while unsuccessful cases look a lot like Bjork’s weak muscled (backward rotating) patients. This means that growth can beneficial when the patient is strong muscled and can be deleterious when the patient is weak muscled. This is another reason to be very careful when treating weak muscled patients.
Again, here are the concepts that Bjork's studies emphasized. The mandible, although strictly speaking is not a long bone like leg or arm bones, grows like one. The amount of growth is genetically determined. How this growth is expressed can be influenced by the control (or lack of control) of the vertical dimension of occlusion. Therefore, to avoid the unsuccessful results as demonstrated in the Tweed Foundation study, one of the major goals of orthodontic treatment is control of excessive molar eruption. This will help minimize backward mandibular rotation. Here's another way of looking at it: the mandible is a beast; it's going to grow no matter what. Our job is to control the direction of growth; the best way to do that is by controlling the vertical dimension of occlusion. Controlling this vertical dimension is much easier in strong muscled patients than in weak muscled patients. To make things easier on yourself, simply refer weak muscled patients. If you feel you are up to the challenge of treating weak muscled patients, use mechanics to help limit excess molar eruption.
Intra Matrix Rotation
In his studies, Bjork also discussed the concept of intra matrix rotation. He defined the intra matrix as the maxillary and mandibular teeth and alveolar processes. The intra matrix rotates in conjunction with, but independent of, the maxilla and mandible. To understand intra matrix rotation, one more definition is necessary. That is the fulcrum. Bjork described the fulcrum as the most anterior portion of the dentition where contact between the maxillary and mandibular teeth occur.
There are three basic types of intra matrix rotation. Type I occurs in strong muscled patients when the fulcrum is at the incisal edges of the upper and lower anterior teeth. This combination of mandibular and intra matrix rotation results in optimal downward and forward growth rotation. If a patient presents with this set of characteristics, the only possible malocclusion possible is a class I crowded situation. The slide below shows an example of a type I intra matrix rotation.
Type II intra-matrix rotation occurs in strong muscled patients where the fulcrum has shifted to the middle of the arch. Because there is nothing preventing anterior eruption, a dental deep bite as a result of excess anterior eruption is often the result of type II intra-matrix rotation. Patients who experience this type of intra-matrix rotation present with class II division II characteristics of occlusion. An example of this is presented in the slide below.
An important question when dealing with this type of intra-matrix rotation is "why does the fulcrum shift?" There are many reasons for a fulcrum shift. They include allergies, airway or breathing problems, tongue, lip and/or finger habits and early loss of primary teeth. These problems (which are mostly environmental) can greatly influence the expression of mandibular growth.
This brings us to the last general category of intra-matrix rotation, which can be called a type III intra matrix. This occurs in weak muscled patients when the fulcrum is in the posterior segment of the arches. The reason for this fulcrum shift could be genetic (down and back mandibular rotation would naturally produce the posterior fulcrum) or environmental (the same reasons as described for a type II intra matrix). No matter what the reason for the shift, this growth pattern can result in two possible outcomes. If the rotation pattern is combined with optimal anterior eruption the result will be a long face but reasonably good occlusion. However, if this rotational pattern is combined with less than optimal anterior eruption, the result will be a skeletal and dental open bite, as seen in the slide below.
With all of these variations in growth and intra matrix rotation patterns, it becomes easy to see why treatment response in different patients (remember the number one rule) occurs. The slide below shows two different patients, one of whom experienced extreme forward mandibular growth rotation with the fulcrum not at the incisal edges of the anterior teeth, and the other who experienced down and back mandibular growth rotation with less than optimal anterior eruption. Everything about these cases is different; do you really expect treatment response to be the same?
Before we end this basic science discussion, one more concept needs to be emphasized. This concept is that all faces flatten as they mature, but the mechanics of flattening differ in forward and backward rotators. It is important to understand that significant flattening of the face occurs as kids grow. When completing a phase 1 treatment, if the patient looks very full, the natural changes to the face that occur as a result of normal development will lead to better facial balance. So, if given the choice, finish phase 1 treatments with the patient looking a little full because that fullness will resolve itself as growth is expressed.
In strong muscled patients, because of the direction of mandibular growth rotation, the chin moves forward but the strong facial musculature prevents the teeth and alveolar processes from moving forward as much as the chin. The result is a flatter face as the patient matures. Look at the slide below to see an example of this phenomenon.
This patient was treated non-extraction; notice the facial changes which naturally occurred as she matured.
In weak muscled patients, faces also flatten but the mechanics are different than those that occur in strong muscled counterparts. Mandibular rotation causes down and back movement of the chin and the retrusive position of pogonion results in a flatter face. The patient shown in the slide below demonstrates this phenomenon.
In conclusion, to effectively treat orthodontic patients, the clinician must understand growth rotation of the mandible and how it affects orthodontic treatment. By studying the work of Sassouni, McNamara, Bjork as well as many other orthodontic researchers, the orthodontic clinician can achieve a good working knowledge of mandibular growth rotation and how this relates to growth and development.
Dr. Prittinen received his DDS degree from the University of Minnesota in 1981. He has been an orthodontic instructor for the United States Dental Institute since 1993 and is a member of the American Orthodontic Society (AOS). In addition, he has been the director of Practical Orthodontics since 1997. Practical Orthodontics is an organization whose mission is to provide orthodontic education opportunities for dentists. Dr. Prittinen maintains a general dental practice in Virginia, MN, where he treats about 50 orthodontic cases per year. Dr. Prittinen has had numerous orthodontic articles and reviews published in “General Dentistry”, the AOS Journal, and many other publications. His website, www.practicalorthoce.com, is a site dedicated to providing orthodontic education to general practitioners who want to learn more about orthodontics.
Start to Finish Veneers: Part 3, Insertion with Adhesive Bonding
As evidenced by the previous two posts in this sequence, planning and preparing teeth for functionally cosmetic restorations is a demanding process that requires diligence, time, and expertise. The provider and patient should both be extremely excited for the final result of the hard work and time that has been invested. Although communication with the laboratory and the skill of the ceramist are critical factors in determining the final outcome, only after careful case planning, meticulous tooth preparation, and successful prototyping of the project, can successful delivery of final ceramics can be considered.
Figure 1; Presentation of patient and provisionals at delivery appointment
The importance of home-care and dental hygiene instructions for the duration of the provisional use is paramount, as an isolated field free of heme and debris is supremely advantageous for inserting cosmetic ceramic restorations with an adhesive bonding technique. Fortunately, the patient in this case was able to maintain good oral hygiene and presented with healthy gingiva that showed little to no sign of inflammation (figure 1). In cases where gingival inflammation will create heme that will interfere with adhesive bonding techniques, placing retraction cord in the gingival sulcus must be considered.
Before removal of the provisional restorations, the patient is anesthetized. This can be done with conventional buccal and facial infiltration techniques, or from the palate in an effort to preserve lip mobility in order to evaluate the smile and presentation of teeth relative to upper lip dynamics.
After the patient is comfortably numb, the provisional restorations are removed. Since a shrink-wrapping technique was used in this case, the provisional restorations are connected. A hemostat is used to crush and fracture the acrylic material in interproximal areas (figure 2). After gross removal of the temporary restorative material, hand instruments like scalers can be used to facilitate complete removal (figure 3a). The preparations are then polished using an oil-free flour of pumice (figure 3c), as the oil content in regular polishing paste commonly used for dental prophylaxis can interfere with bonding.
Figure 2; Crushing the provisionals with a hemostat to break them and facilitate removal.
Isolation of the operative field is an essential component of performing adhesive dentistry. Rubber dam isolation is most likely considered ideal for achieving maximum isolation. For this case, an OptraGate (Ivoclar Vivadent) was used to isolate the operative field and provide retraction of soft tissues (figure 4).
Figure 4; Isolated field with retraction using an OptraGate (Ivoclar Vivadent).
Glycerin based try-in pastes are consistent in shade with the final resin cement.
Composite resin cements are consistent in shade with the glycerin based try-in pastes.
After the ceramics have been evaluated and verified for fit and composition on a stone model, individual ceramics are placed intra-orally to confirm marginal fit using visual evaluation and tactile inspection with a dental explorer (figure 5a, 5b). After the marginal adaptation and fit of each restoration is confirmed to be satisfactory, all restorations are placed onto the respective preparations with a water soluble glycerin based try-in paste (Variolink Esthetic, Ivoclar Vivadent) to evaluate interproximal contacts and the esthetic presentation of the adjacent grouping in situ (figure 5c, 5d, 5e, 5f, 5g). The advantage to the try-in pastes is two-fold. First, the paste will retain the restorations well enough for the patient to evaluate the shade and shape of the teeth, and the composition of the new smile. The patient should examine the ceramics in different light sources to ensure the effects of metamerism will not dramatically or adversely influence the shade presentation of the restorations. Second, the try-in paste will offer a replica of the final cement shade and any influence it may impart of the optics of the final restorations, namely the quality of color relating to value. In this case, the operator has three choices of try-in cements: “neutral,” which is desirable as it will impart no change on the presentation of the ceramics; “warm,” to lower the value if the restorations appear to bright; and “light,” to increase the value of the restorations if they appear to dull. The final resin cement should match the try-in paste that was confirmed during the trial arrangement. The try-in pastes are water soluble, and will rinse away will no effect on the final bond strength.
Figure 5g; Adjacent grouping of all ceramics placed in situ.
After all aspects of a cosmetic try-in are completed, and all elements of the try-in are satisfactory to the provider and patient, the steps for adhesive bonding insertion can commence.
The ceramic preparation should start at the laboratory. Ceramic materials must be etched with a hydrofluoric acid if they are to be adhesively retained. For this case, the lithium disilicate material that was chosen (eMax, Ivoclar Vivadent) was etched for 20 seconds with 5% hydrofluoric acid before being thoroughly rinsed and dried, per the manufacturer’s instructions. The parameters for the strength of HF acid and duration of contact with the ceramic vary depending on material, but the effect is the same: the acid dissolves glassy components within the crystalline matrix to create micromechanical retention via tunnels and grooves necessary for adhesive bonding. In a similar way to etched enamel, the surface of the ceramic should subsequently appear slightly frosty but clean, with no precipitate residue or cracks (figure 6a, b). After the ceramics are tried-in intra-orally, they are considered contaminated and must be cleaned prior to further preparation and delivery to ensure a high bond strength. Although reapplying 5% HF acid will sufficiently clean the intaglio surface of the restoration, HF acid is extremely caustic and has special handling considerations. Furthermore, over-etching the ceramic can create salt precipitates that interfere with bonding. Over-etching can also weaken the structural integrity of the ceramic. An alternative to re-etching with HF acid is to use a metal-oxide based cleaner with a high affinity for the phosphate chain groups that contaminate the surface to be bonded and interfere with adhesion. For this case, IvoClean (Ivoclar Vivadent) was used to remove phosphate chain groups and clean the restorations by coating the intaglio surface of each restoration for 20 seconds before being rinsed thoroughly with water and dried with an air-only syringe (figure 6c). In the case that an operator does not have these specialty items available, 37% phosphoric acid etchant can be used to coat the intaglio surface of the restoration for 60 seconds before it is rinsed and placed in water and an ultrasonic bath for five minutes. To improve bond strengths and bond durability over time, a silane coupler is applied to the clean ceramic restorations (figure 6d). By applying a silane methacrylate to the ceramic material, a chemical reaction occurs that creates a methacrylate silicate compound capable of cross-linking the silica content in the ceramic restorations with the methacrylate content in the resin cement. Multiple coats may need to be applied, and the chemical reaction will take at least 90 seconds. At this point, the ceramic restorations are fully prepared for insertion with an adhesive bonding technique, and are organized according to tooth number to avoid confusion during the procedure.
After the ceramics are adequately cleaned and prepared, the tooth structure must be prepared to receive the restorations in kind. Adequate isolation of the surgical field is required. In this case, an Optragate was used, but a solid argument can be made that a rubber dam would be the standard of care for proper isolation to employ and adhesive bonding technique. Selection of materials is paramount here, as there are a number of adhesives and resin cements on the market for the application of bonding indirect restorations to natural tooth structure. Multiple generations of adhesives and multiple iterations of resin cements have the potential to make adhesive dentistry confusing (figure 7a, 7b). When bonding to natural tooth structure, the core principles remain the same. Dentin must be etched adequately using an acid etchant. Enamel must be etched adeuately using an acid etchant.. A hydrophilic monomer (primer) must be used to infiltrate partially collagenous dentinal tubules for an appropriate amount of time. A hydrophobic monomer (adhesive) must be used to complete the formation of a hybrid layer that will link tooth structure to the methacrylate groups in composite resin cements. Moisture control and the absence of contaminants is paramount. Specific instructions and use indications will differ between the various adhesive systems and cements. It is the responsibility of the provider to use adhesive bonding systems that are compatible with the resin cement of choice.
Figure 7a
Figure 7b
The teeth are reinspected for debris or residual material and carefully polished again with oil-free flour of pumice paste.
The tooth surfaces to be bonded are etched adequately using a 37% phosphoric acid etch. If using a total etch system, the duration of etching is 25 seconds. Even in cases where an All-in-One or Universal adhesive system is utilized, etching the enamel separately is wise to ensure adequate etch. The tooth structure is rinsed for 20 seconds and then dried thoroughly using an air-only syringe. In this case, a universal adhesive (Adhese Universal Viva Pen, Ivoclar Vivadent) was applied to each tooth for 20 seconds each. The solvent was gently evaporated using an air-only syringe before being light cured for 10 seconds on each tooth. The adhesive does not necessarily need to be cured prior to insertion, but complete polymerization of the bond before insertion with a light cured resin cement will yield a higher final bond strength. Although a dual-cure cement with a compatible adhesive can be used to insert veneers, working time will become a concern with this choice, as the chemical cure of the material will commence and complete within a pre-determined amount of time.
Dr. Ryan J. Yakowicz, DDS, FAGD
Dr. Yakowicz practices in the Greater Madison Area of South Central Wisconsin. Having completed over 800 hours of continuing education, his special interests include functionally cosmetic full mouth rehabilitation, TMD and oral-facial pain, and surgical implant placement and prosthetic restoration.
Dr. Yakowicz is currently the president of the Madison Dental Progress Forum Study Club and the Wisconsin Institute for Advanced Dental Education. He is a Fellow of the Academy of General Dentistry, and a member of the American Academy of Cosmetic Dentistry, and the American Academy of Fixed Prosthodontics. Additionally, Dr. Yakowicz participates in research studies for the National Provider-Based Research Network and is an Ambassador to the National Health Service Corps.
Phasing Complex Treatment for Adolescent Patients with Orthodontic Needs
Patients presenting to to the dental office with widespread enamel defects or congenital enamel hypoplasia can present unique challenges for an operator charged with restoring the compromised teeth to proper form, function, and esthetics. These challenges are exacerbated when the patient is young or adolescent, as transitions through the mixed dentition phase and long-term appositional downward and forward growth of the maxillo-mandibular complex must often be considered. Perhaps one of the most demanding cases to address is a patient who presents with multiple criteria listed above and is in need of orthodontic treatment (figure 1a, 1b, 1c). Addressing compromised hard tissue is paramount in treating these cases, as establishing oral health will provide the basis for numerous future treatment modalities. Moreover, poor enamel quality can compromise the ability of the orthodontic provider to bond brackets when clear aligners are insufficient to address orthognathic discrepancies.
Figure 1a; A panoramic radiograph of the patient
Figure 1b; A cephalometric radiograph of the patient
Figure 1c; A retracted (1:3 magnification) view of the patient’s dentition pre-treatment
The following patient (a 17 year old male) presented with chief complaints related to his bite and the appearance of his teeth. The patient and his parent were both aware of the poor enamel quality, since older siblings have experienced the same condition. Upon initial exam, the following dental problem list was developed:
® Poor enamel quality relating to poor oral health and high caries risk
® Poor enamel quality for bonding orthodontic brackets
® Altered passive eruption
® Abnormal tooth morphology
® Dental caries, attrition, and fracture of tooth structure
® Retained primary teeth O and P with no succedaneous teeth
® Conjoined supernumerary tooth associated with the upper left second bicuspid
® Skeletal inequity affecting facial profile and causing occlusal discrepancy
® Fair oral hygiene and gingival inflammation
® Impacted third molars (#1,16,17) and upper right second molar (#2)
® Dental esthetics
(figure 2a, 2b, 2c)
Figure 2a; A retracted right lateral view (1:3 magnification).
Figure 2b; A view of the maxillary anterior teeth (1:1 magnification).
Figure 2c; An occlusal view (1:3 magnification). Note the conjoined supernumerary tooth on the mesial aspect of the upper left second bicuspid.
The patient was referred to the orthodontist for further evaluation, and the following orthodontic findings were reported:
® Class II Malocclusion
® Poor spacing and tooth size discrepancy
® Severe overjet with deep, impinging overbite
® No TMJ problems found
® Centric Relation appears to be equal to Centric Occlusion
An orthodontic treatment plan was developed. Comprehensive orthodontics was recommended, with a focus on utilizing elastics and Forsus appliances to correct the Class II occlusion. Surgical mandibular advancement would be considered if non-surgical modalities proved to be insufficient in correcting the Class II occlusion. Initially, bite blocks were treatment planned to open the deep bite, but it was decided that an increase in Vertical Dimension of Occlusion (VDO) could be accomplished within the context of the restorative plan. Impressions were taken and casts were made and digitized (figure 3a). Case planning was done in combination with the restorative doctor, the orthodontist, and the digital dental laboratory technician by utilizing 3Shape Software and Computer Aided Design (CAD) (figure 3b).
Figure 3a; Digitized pre-operative models.
Figure 3b; CAD / CAM design of the case.
The main goals of the restorative plan were numerous and varied. Establishing oral health by removing compromised hard tissue was foundational to the success of the treatment plan. Restoring the teeth to proper form, function, and esthetics after the surgical removal of affected and infected hard tissue was considered essential to successful treatment. The restorative plan included not only esthetic correction within the limitations of the existing orthognathic condition, but also an increase in VDO to accommodate orthodontic movement of the anterior segments to correct the deep bite. The teeth needed to be restored individually to give the orthodontic provider control over root and tooth movement. Additionally, the teeth would need to be restored with a material suitable for accommodating adhesive bonding of orthodontic brackets. A final consideration in the initial restorative therapy was to provide the patient with semi-permanent restorations, as the changes to occur through orthodontic treatment and continued appositional growth would undoubtedly alter the location and presentation of the teeth within the maxillo-facial complex. Composite was selected as the most suitable restorative material to achieve the initial treatment goals. The patient was made aware that ideally, the composite crowns would be replaced sequentially with definitive dental ceramics after a proper orthodontic end point was achieved and growth was complete. Additionally, gingival plastic surgery was indicated to address the altered passive eruption, as 5-7 mm of soft tissue was present between the alveolar crest and gingival margin of multiple teeth. For initial therapy, gingivectomies with internal beveling and trans-sulcular crown lengthening would be performed to increase tooth length and maintain biological width (figure 4). Primary teeth O and P were incorporated into the restorative plan. It was decided these teeth would be retained as long as possible before extraction and definitive replacement with implants or a fixed partial denture. Initially, endodontics and removal of the supernumerary tooth conjoined to the mesial of tooth #13 was considered. After CBCT evaluation of pulp horn location, it was determined that the conjoined teeth would be treated as a single tooth, and preparation design would include the supernumerary tooth, despite a small esthetic compromise due to excessive mesial-distal width (figure 5a-b).
Figure 4; Representation of the dentogingival complex (biologic width).
Figure 5a; CBCT evaluation of tooth #13 and conjoined supernumerary tooth, along with the proposed restoration design.
Figure 5b; The modified preparation of conjoined supernumerary tooth
It was decided that the restorative plan could be used to increase the VDO to facilitate orthodontic movement of the anterior segments by creating space. Although it is arguable that this should be the primary reason for an increase in VDO, it is important to consider that bite blocks would have been implemented to create a vertical increase anyway. Additionally, it was apparent that tooth structure had been lost due to caries, fracture, or attrition in the posterior, suggesting a collapse in verticality had occured, and that replacing the lost vertical dimension should be part of restoring the posterior teeth. Caution should be implemented in increasing the VDO of patients with Class II occlusion and deep bite. As the vertical dimension (overbite) is increased, so too is horizontal dimension (overjet). This can cause problems related to speech and mastication (especially incising food) if the increase is too great. For this patient, who initially presented with a severe overbite and is committed to undergoing orthodontic treatment to better relate the anterior segments, the potential for temporary negative effects was a tolerable risk to facilitate the final outcome. As previously stated, the VDO was increased largely to give the orthodontist room to re-position anterior segments of upper and lower teeth, thereby providing the operator and lab technician with only a broad target range of how much vertical space to create. General guidelines related to increasing VDO were followed, and a 4 mm increase in VDO was agreed upon by the general dentist and orthodontist.
To address the collapsed dentition and skeletal deep bite, the maxillary central incisors and maxillary canines provided key information for planning the case. Commonly, the central incisors can help discern the amount of vertical increase needed. As a guideline, a measurement taken from the Cemento Enamel Junction (CEJ) of the maxillary central incisor to the CEJ of the lower central incisor should be 16 - 18 mm in a Class I patient and 14-16 mm in a Class II patient. These measurements can provide guidelines (not justification) for the necessity and amount of vertical increase; if the CEJ - CEJ measurements are collapsed (less than the average values) an increase in VDO may be necessary (in a standard patient). The dimension of the patient’s central incisors was deficient, especially in length, and diastemas were present. The CEJ-CEJ measurement was only 11 mm (figure 6). Increasing incisal length was done minimally and judiciously to create symmetry, as the position of the central incisors and incisal edge in the patient’s face was appropriate. Tooth length gain could however be accomplished in an apical direction by performing gingivectomy with internal beveling. When sounding bone, it was discovered that the alveolar crest was located 4 - 6 mm from the gingival margin in the anterior segment, confirming that the actual CEJ of the maxillary central incisors is positioned more apically than the gingival margin would suggest. By relieving 3 mm of soft tissue and severing the connective tissue attachment, a 3 mm gain in tooth length could be achieved while still providing 3 mm for biologic width. In areas where 3 mm of space to accomodate biologic width was not available, a chisel was used to remove small amounts of the crestal bone through the sulcus (figure 7a-e). A new measurement from CEJ-CEJ would then be 14mm, which is more normative for a Class II patient. Only the canines were treated with plastic surgery at the time of initial treatment. Although evaluation of the dento-gingival complex relating to the central and lateral incisors was essential for treatment planning, it was decided surgery would be done after re-evaluation when a stable orthodontic endpoint was reached and growth was complete.
Figure 7a-e; a) Periodontal probe reading of the sulcular depth is 3 mm. b) When sounding bone, the periodontal probe reading approaches 6 mm. c) Gingivectomy to relieve excess tissue and contour gingival shroud (note the amount of enamel apical to the initial gingival margin posititon). d) Internal bevel to sever the connective tissue attachment. e) a bone chisel with a laser etched 3 mm marking to ensure adequate space for biologc width between the crestal bone and the new gingival margin position.
As detailed by Dr. Carl Misch, the canine position is a key indicator for planning tooth position relative to the maxilo-facial complex. Although some apical gain could be created by performing gingivectomy on the canines, it was clear that orthodontics would be required to continue apical movement to position the teeth (especially the canines) in the proper location. Although 3 mm worth of gingivectomy could help with the canine tooth length, apical gain alone would not be adequate to position the teeth correctly in the maxillo-facial complex. The acceptable range for canine exposure in relation to the maxillary lip line varies, but Misch found that the range of canine display in a lip at rest position varies far less than that of central incisors. Our goal for the patient was to have 0-1 mm of the canines visible in a lip at rest position. Gingivetomy with internal bevel and trans-sulcular bone removal was to be performed, but it was determined that the canine would still need to move apically 3 mm to be in the proper location in the face. Because the initial restorative phase would be interim in nature, the VDO change could be adjusted as necessary; either to accommodate orthodontic movement or to relieve possible TMD symptoms due to the patient being unable to accommodate the new VDO.
Figure 6; CEJ-CEJ measurement (11 mm) and maxillary right central incisor measurement (8 mm long x 8 mm wide).
Overall, the case was designed as a full mouth rehabilitation. The design included considerations related to tooth proportion, gingival zenith location, increased vertical dimension, esthetic correction, and stable occlusion. The plan was representative of initial therapy with the intention of being revisited after completion of orthodontic treatment.
Transfer of the plan to the patient’s dentition was completed using deliverables from the dental laboratory and composite resin. In the Computer Aided Design / Computer Aided Manufacturing (CAD / CAM) software, the complete design of the corrected maxillary and mandibular arches was printed using a 3D printer. Then, the initial design was altered so that only every-other tooth was corrected, while every-other tooth remained in its pre-operative state (figure 8). A set of models representing a correction of every-other tooth for each arch was also printed. Clear matirces were made on each set of models. Clinically, the patient was anesthetized, and soft tissue corrections were made using a 15C Scalpel and bone chisel. Next, every-other tooth was treated by removing unhealthy hard tissue before being prepared for the composite restoration. Retraction cord was placed in the gingival sulcus of the prepared teeth. The unprepared teeth adjacent to the prepared teeth were protected with strips of sterilized polytetrafluoroethylene (PTFE) tape to prevent unintentional adhesive bonding. A 37% phosphoric acid etch was used in a total etch technique, desensitizer (MicroPrime G, Danville) was applied to the prepared tooth structure and adhesive (Prime&Bond Elect Universal Dental Adhesive; Denstply Sirona) was applied for 20 seconds and light cured for 10 seconds. The clear matrix was fit over the unprepared teeth and shade A2 flowable composite (Herculite Ultra-flow Nano-hybrid; Kerr) was injected through a porthole created in the matrix prior to placement (figure 9a-d). The composite was cured through the matrix for 20 seconds on each surface; the excess material was trimmed and the restorations were contoured before the next set of teeth were prepared (figure 10a-b). This process was repeated for the remaining teeth. The occlusion was adjusted as necessary and the final composition was then polished. The patient was re-appointed for a 3-week re-evaluation to ensure the increase in vertical dimension was not problematic, and that stomatognathic functions such as eating, swallowing, and speaking were not compromised.
Figure 8; The “every-other” model in CAD / CAM software.
Figure 9a-d;
Figure 10a;
Figure 10b;
Ultimately, each tooth was restored individually to enable individual orthodontic root and tooth movement while providing a bondable substrate for orthodontic brackets. Although provisional, the restorations offered the patient immediate improvements in oral health, and in the form, function, and esthetics of his teeth. Furthermore, because the restorations are not considered definitive, the prototype is dynamic and able to be altered during continued restorative and orthodontic treatment; unlike dental ceramics, composite can be easily removed from or added to. Furthermore, the living prototype will provide valuable information before the dentition is to be definitively restored. Although cases like these require intensive planning pre-clinically and many chair hours clinically, the initial improvements are extremely rewarding. Given proper treatment planning and coordination between the operator, orthodontist, and lab, cases like this can be extremely fun to execute!
Dr. Ryan J. Yakowicz, DDS, FAGD
Dr. Yakowicz practices in the Greater Madison Area of South Central Wisconsin. Having completed over 775 hours of continuing education, his special interests include functionally cosmetic full mouth rehabilitation, TMD and oral-facial pain, and surgical implant placement and prosthetic restoration.
Dr. Yakowicz is currently the president of the Madison Dental Progress Forum Study Club and the Wisconsin Institute for Advanced Dental Education. He is a Fellow of the Academy of General Dentistry, and is a member of the American Academy of Cosmetic Dentistry, and the American Academy of Fixed Prosthodontics. Additionally, Dr. Yakowicz participates in research studies for the National Provider-Based Research Network and is an Ambassador to the National Health Service Corps.
References:
1) Spear, F (2006) Approaches to Vertical Dimension. Advanced Esthetics and Interdisciplinary Dentistry 2 (3): 2006: 2-12.
2) Kois, J, Phillips, K (1998) Occlusal Vertical Dimesnion: Alteration Concerns. Compendium 18 (12): 1998: 1169-1177.
3) Rivera-Morales WC, Mohl ND. Relationship of occlusal vertical dimension to the health of the masticatory system. J Prosthet Dent. 1991 Apr;65(4): 547-53.
4) Terry, Douglas A., Willi Geller, and Douglas A. Terry. 2013. Esthetic & restorative dentistry: material selection & technique. Chicago: Quintessence Pub. Co.
5) Misch, CE. Guidelines for maxillary incisal edge position-a pilot study: the key is the canine. J Prosthodont. 2008 Feb;17(2):130-134.
6) Terry D, Powers J, Blatz M. The Inverse Injection Layering Technique. Journal of Cosmetic Dentistry. 2018 Spring; 34 (1): 48-62.
7) Coachman, C. Emotional Digital Dentistry. Journal of Cosmetic Dentistry. 2019 Winter; 34 (4): 36-42.
8) Lyons, L, English, J. In Vitro Shear Testing of Orthodontic Bonding to Lithium Disilicate Ceramic. Journal of Cosmetic Dentistry. 2019 35 (1): 82-89.