Sunday, July 31, 2011

A Note On Use of Resorbable Plates and Screws in Pediatric Facial Fractures.......with pdf Download

The pediatric facial trauma patient provides several different considerations that are not present in the adult. First, the pediatric patient has the tremendous advantage of an accelerated ability to heal in a very short time with few complications, aided by the well-vascularized tissues of the face. Second, through the assistance of growth and an inherent ability to adapt, recovery of damaged orofacial tissues and function is much better than in the adult. Despite these advantages, certain distinctions do exist in the pediatric facial trauma patient that must be considered. This includes an appreciation of the unique characteristics and anatomy of the developing immature face, the different facial injury patterns from certain trauma risk exposures that occur in the pediatric patient, and the potential growth implications from traumatized facial structures that make long-term follow-up of these patients important. These factors, combined with the relatively limited experience of most clinicians with significant facial injuries in children due to their low incidence, may make certain treatment decisions different than what one might do in the adult. In this post, the term pediatric facial fractures will refer to fractures in those children under the age of 10 with an incomplete permanent dentition. Children older than 10 years of age are essentially treated as adults, where the advantages of resorbable fixation over metal implants are in many cases more obscure.

Resorbable Fixation Devices
Although a variety of resorbable bone fixation devices of differing polymer compositions are currently available for craniomaxillofacial applications, this author has exclusively used co-polymer plates and screws composed of 82% polylactic and 18% polyglycolic acid (PLLA-PGA, LactoSorb; Walter Lorenz Surgical, Jacksonville, FL). Their long history of uncomplicated use in cranial vault surgery, favorable biomechanical properties, and a confirmed  resorption time of 1 year or less make them ideal for the pediatric patient. The use of resorbable plates and screws involve 2 differences from similar-appearing metal devices. First, complex bending of the plates requires a heat source to allow the polymer chains to bend and not fracture. The mandible and forehead, however, have relatively flat and gently curved surfaces, which do not require enough bending to make this a concern. In the zygoma and orbit, more complex shaping of the plates may be needed. The placement of resorbable screws requires pretapping the screw threads before screw insertion, which is a 2-step process (ie, drilling and tapping).

Mandible Fractures
FIGURE 1. Resorbable plate and screw fixation (1.5 mm) of bilateral mandible fractures in a 4-year old girl. A, Reduction of left parasymphyseal 
fracture. B, Reduction of right angle fracture with a superior border plate. C, Centric occlusion obtained by free hand technique.



Pediatric mandible fractures are uncommon and have been treated by a wide variety of fixation methods. Incomplete or nondisplaced fractures as well as fractures of the subcondylar region are treated by traditional methods of a soft diet or closed reduction. Displaced fractures are better served by open reduction and internal fixation (ORIF).
Rigid metal fixation of mandibular fractures in children, however, can be complicated by a mixed dentition that can occupy the entire vertical dimension of the bone and places teeth and the inferior alveolar nerve at risk during screw insertion. In addition, on-going development of the mandible poses risk of intrabony translocation of metal plates and screws, risking potential growth and teeth disturbances and difficulty with secondary removal if needed. The goal of ORIF is a balance between stability of the fracture site and the potential risks of operative exposure of the bone. In children, this balance is particularly precarious as the implantation time of the metal devices is essentially for most of the patient’s lifetime. For these reasons, the use of resorbable fixation implants in developing facial bones is particularly appealing. Given the location of mixed dentition throughout the bone and the course of the inferior alveolar nerve, ORIF of the mandible in children uses smaller-gauge resorbable miniplates with monocortical screws. As the pediatric mandible is fairly malleable, fractures tend to be less displaced and rarely comminuted. Because the dentition is often mixed and more bone growth is expected, absolute compression of the fracture edges together is not necessary. These considerations, in conjunction with the difficulty in applying arch bars in the mixed dentition, allows for the use of a free hand technique during fracture repair. Fractures are usually exposed through an intraoral approach unless an existing laceration allows for direct access to the bone through the skin. Once the fracture site is prepared, the bone edges are manually reduced while the dentition is held together in centric occlusion by an assistant. A 1.5-mm resorbable plate with at least 2 screw holes on each side of the fracture is held along the inferior border of the mandible in tooth-bearing regions. A short drill bit (1.1 mm in diameter, 5 mm in length) is used to place bone holes through the desired screw positions on the plate. The drill holes are through the outer cortex only so as to avoid drilling into unerupted teeth. A hand-held tap (1.5 mm) is then used to cut the screw threads. Resorbable screws (1.5 mm in diameter, 4 or 5 mm in length) are inserted until flush with the plate (Figs 1, 2 ). In most cases, 1.5-mm plates usually provide adequate fixation.
FIGURE 2. Resorbable plate and screw fixation (1.5 mm) of severely displaced left mandibular parasymphyseal fracture in a 5-year-old boy. A,Magnitude of mandibular arch displacement. B, Intraoral exposure of fracture. C, Reduction and fixation of fracture with 1.5-mm plates and monocortical screws. D , Postoperative panoramic radiograph showing fracture alignment and screw holes around developing tooth buds.


The free hand technique for maintaining a centric occlusion before plate fixation works fairly well for most isolated pediatric mandibular fractures. However, alignment of the visible buccal cortex does not always guarantee a perfect occlusal result, particularly in mandibular injuries with obliquely oriented fractures. In these fracture patterns, the lingual cortex may be misaligned and a gap on this side of the mandible may persist. Unlike fixation with more rigid metal plates, resorbable plates cannot really be overbent and their physical properties merely allow them to lie passively against the bone. Such lingual misalignment cannot be easily corrected by these less rigid resorbable plates. Because this classic principle of mandibular fixation cannot be effectively used, it is therefore important to carefully check occlusal interdigitation after resorbable plate placement.
When mandibular fracture alignment cannot be easily reduced or held properly in centric occlusion, an  alternative technique is to place temporary wire ligature reduction across the fracture site (Fig 3 ). In this technique, which may require a transcutaneous approach, metal screws are placed along the inferior border and a wire ligature is placed between them to reduce the fracture. While the reduction is held in this manner, a resorbable plate is then placed on the buccal cortex along the inferior border. The wire reduction devices are subsequently removed.
FIGURE 3. Inferior border reduction technique before plate application in right mandibular parasymphyseal fracture in an 8-year-old boy. A, Fracture exposure through cervical skin incision. B , Fracture reduced by inferior border metal screws and wire ligature. C, Shows 2.0-mm plate and screw fixation. D , Metal screw and wire ligatures removed before closure.


One significant advantage of resorbable screws in the pediatric mandible is the avoidance of potential odontogenic injury. As the drill hole and tapping of the screw threads penetrate only the outer cortex, injury to developing teeth is unlikely. Even if the resorbable screw tip encroaches upon a tooth, its tip is blunt and nonpenetrating. Subsequent resorption of the screw removes any potential obstruction to tooth eruption. As such, resorbable plates and screws may be applied in even the youngest mandible, where the entire bone is composed entirely of teeth and nerve (Fig 4).








FIGURE 4. Resorbable plate and screw fixation in mandibular symphysis fracture in 3-week-old male infant. A , Fracture exposure through chin laceration. B , Shows 1.5-mm plate and screw fixation. C, Post-operative radiograph showing fracture alignment.

























Saturday, July 30, 2011

A Note On Non-Carious Tooth Substance Loss and PDF Download....v

Non-carious tooth surface loss is a normal physiological process occurring throughout life, but it can often become a problem affecting function, aesthetics or cause pain. This loss of tooth structure or wear is often commonly termed abrasion, attrition, erosion and abfraction. Often, this wear is a complex combination of these and there is difficulty identifying a single aetiological factor. Diagnosis, prevention and treatment should be based on these multifactorial causes.

Causes
Knowledge of the aetiology is important for preventing further lesions and halting the progression of lesions already present. In addition, treatment will be ineffective in the long term unless the aetilogical factors are eliminated.
Here is a discussion of the common causes:
1. Congenital abnormalities:
Amelogensis and dentinogenesis imperfecta (Figure 1) may cause regressive changes in teeth and extensive tooth wear can result from normal function.

2. Attrition:
Is the loss of tooth structure or restoration caused by mastication or contact between occluding or interproximal surfaces. It primarily affects occlusal or incisal surfaces, but slight loss can occur at the contact points. This type of tooth wear can be significant in patients with “primitive diets” e.g. the aboriginal population - high quantity of dietary abrasives (Molnar et al, 1983). However the most common cause of attrition is probably parafunctional activity such as bruxism (Figure 2) (Smith BGN, 1989 and Dahl et al, 1975).

3. Abrasion:
Is the loss by wear of tooth substance or restorations caused by factors other than tooth contact. Rubbing of pipes, hairclips, musical instrument mouthpieces, excessive tooth picking, etc, could cause this. The most common cause is incorrect or over-vigorous tooth brushing (Figure 3).

4. Erosion:
 Is the progressive loss of dental tissue by chemical means not involving bacterial action. Acid is the most common cause of  erosion demineralising the inorganic matrix of teeth.

5. Dietary erosion: 
May occur from food and beverages like fruit juices and soft drinks, which are highly acidic. The potential for erosive damage by these beverages may not be well understood by the public. Another source of dietary acids are orally administered drugs like chewable vitamin C tablets, aspirin, iron tonics and replacement HCl used by patients with gastric achlorhydria (Levith et al, 1994). Winetasters also often present with significant.

6. Regurgitation erosion (Voluntary and involuntary):
 Is the return of gastric contents to the mouth. This is highly acidic (pH 2) and erosive. Repeated episodes may be more problematic.
          a. Involuntary regurgitation:  or gaestroesophageal reflux can occur due to hiatus hernia or as a consequence of pregnancy or chronic alcoholism.
          b. Voluntary regurgitation: is usually associated with an underlying psychological problem. Eating disorders commonly associated are anorexia nervosa and bulimia nervosa. The effect of acid regurgitation in bulimic patients often exhibits perimolysis  erosive lesions localized to the palatal aspect of maxillary teeth (Figure 4). Often the pattern of tooth wear in these patients is additionally affected by other factors like consumption of diet beverages and erosive foods (as patients strive to control their weight), xerostomia, caused by vomit-induced dehydration or drugs such as diuretics, appetite suppressants and antidepressants (Hellstrom 1977).

7. Environmental erosion:
 Patients that are exposed to acids in the workplace, e.g. battery factory workers have shown a higher prevalence of erosion in Ger-many and Finland (Tuominen M 1989). Exposure to high levels of hydrochloric acid can also occur in improperly maintained swimming pools.

8. Abfraction: 
Are cervical abrasive lesions thought to be caused by occlusal stresses. The tooth can flex causing tensile and compressive forces at the necks of teeth resulting in cracks in the enamel (Figure 5).

9. Restorative materials: 
The use of porcelain can accelerate tooth wear, especially if this porcelain is unglazed and rough/unpolished (Mahalick JA et al, 1971). Newer materials have been developed like the low-fusing porcelains, which have a finer particle size and exhibit similar wear as natural tooth structure. Metal occlusal surfaces are also recommended for those patients with severe wear or bruxism.

10. Saliva and dry mouth:
 Xerostomia may follow radiotherapy, medications, etc, and may produce both rapid caries and dental erosion. Because the acids are not well-buffered and not diluted by saliva, patients may suffer from erosion. In those patients who displayed accelerated tooth wear, there is strong evidence for a critical role of saliva, particularly of resting salivary pH. There are several reasons for a link between salivary dysfunction and tooth wear:
    • Reduced clearance of dietary acids;
    • Reduced pH of saliva;
    • Reduced buffer capacity, preventing both dietary and also endogenous acids from being neutralized;
    • Reduced remineralisation of surfaces; and
    • Softening of tooth structure leading to accelerated wear from normal wear and tear under occlusal and incisive forces, and labial wear from tooth brushing.

11. Body image:
Attempts to control body weight may influence patients to consume acidic foods, such as fruit and diet drinks. This struggle to achieve the ideal body weight may also increase the prevalence of eating disorders.

12. Loss of posterior support:
 It has been suggested that there is an increase in force per unit area in the remaining dentition, thereby causing an increase in tooth wear. A review of the literature does not support this assumption (Kayser and Witter, 1985).

13. Drug use:
Can be another cause of bruxism and has an effect on attrition and dehydration leading to possible erosive conditions.

Diagnosis
Diagnosis involves a need to identify  the factor(s) contributing to tooth wear. This is to preserve the remaining  dentition and to improve the long-term prognosis of any restorative treatment completed. An initial comprehensive examination is performed, including a thorough medical and dental history and an orofacial and dental clinical exam. Radiographs and other special tests may then be carried out. Such tests may include saliva tests, fracture finder, pulpal sensibility testing, etc.
Questions regarding diet, lifestyle, medications, stress, brushing habits, consumption of sports drinks, etc, can help in aiding diagnosis. Saliva testing may be appropriate; a food diary may also be required. A classification of wear can be made from clinically observed features and habits and careful collation of all this information is required to determine the risk factors and educate patients to help minimize long term damage by tooth wear.
Diagnosis needs to also be made as to whether the wear is physiological or pathologic? If wear has produced an unsatisfactory appearance, sensitivity, reduction in facial height and vertical dimension of occlusion then tooth wear is considered pathologic and this may constitute the need for treatment. A period of monitoring may be required to decide on appropriate management.
This monitoring may be carried out by:
    • Photographic records;
    • Measurements of teeth;
    • Study model comparison;
   • Tooth wear index;
   • Impression of splint and comparison of changes over 3 months;
   • Indices: Erosive tooth wear from a clinical view is a surface phenomenon,
occurring on areas accessible to visual diagnosis. Diagnosis is therefore a visual rather than instrumental approach and can be compared with different
Tooth Wear Indices - Indices by Eccles (1979) and Smith and Knight (1984)(Table 1).

 Prevention
Causes of tooth surface loss must be understood to adopt appropriate preventive measures. Abrasive effects of aggressive tooth brushing can be reduced with education, but can be difficult to change especially with in-built memory. Patients must be informed of correct technique and to use a soft brush. Preference for abrasive dentifrice may need to be changed to a low abrasive one. Other abrasive habits can also be changed like pipe smoking, aggressive use of interdental sticks, etc.
Erosive effects may require change in dietary intake to minimize acidic drinks/foods. Regurgitation erosion is difficult to prevent and some chronic cases require referral. Milder cases are normally controlled with self-medication and dietary control. Counseling may be offered for those concerned with body image or suffering from eating disorders.
Patients must be advised to not brush immediately following acid intake or regurgitation but to rinse their mouth carefully. These patients may also benefit from a fluoride mouth rinse and/or higher fluoride concentration toothpaste. There has also been reports that the use of Toot Mousse (GC) helps neutralize acid challenges from acidogenic bacteria in plaque and other internal and external acid sources. The CPP-ACP molecule binds to biofilms, plaque, bacteria, hydroxyapatite and surrounding soft tissue, localizing bioavailable calcium and phosphate.
Erosion can often be exacerbated by a reduction in salivary flow and investigations like saliva testing may provide information to prevent dehydration and help stimulate salivary flow. Chewing sugar free gum may help in boosting saliva flow.
Bruxism and attrition may be prevented with the use of occlusal splints and stress management. Occlusal adjustment and addition with restorations may also be required.
Monitoring of all preventive measures needs to be performed even if no restorative treatment is performed as to the effectiveness of the program to ensure long-term success and maintenance for patients suffering from tooth surface loss.

Friday, July 29, 2011

A Note On Mandibular movements and definition of terms.... with 3D Animated Mandibular Movement Videos

The movements that the mandible can make and the  names  of  the  important  positions  within  this range  of  movements  are  following  videos
                                                                 Sagital Plane           

                                                          3D Illustration
Terminal hinge axis (THA) and  the retruded arc of movement (or closure)
This  is  an  axis  which  passes  through  both condyles and about which the mandible rotates in its  most  retruded  (comfortable)  position  of  the condyles    the  retruded  arc  of  closure.  This is a clinically reproducible movement and recording it is often useful in making crowns and bridges and essential in making complete dentures. The THA can  be  measured  in  individual  patients  but  it  is sufficient for most applications to use an average THA  such  as  that  recorded  by  an  ear-bow.

Intercuspal position (ICP)
This  is  the  position  of  maximum  contact  and maximum  intercuspation  between  the  teeth.  It  is therefore  the  most  cranial  position  that  the mandible  can  reach.  The  term  ‘centric  occlusion’ has  been  used  to  describe  this  position,  but  this is confused with ‘centric relation’ (see below) and may also imply centricity of the condyles in their fossae,  centricity  of  the  midline  of  the  mandible with  the  midline  of  the  face,  or  centricity  of  the cusps  within  the  fossae  of  the  opposing  teeth, none of which may be the case. The term ‘centric occlusion’ is  therefore  better  not  used.

Retruded contact position (RCP)
This  is  the  most  retruded  position  of  the mandible with the teeth together. It is a clinically reproducible  position  in  the  normal  conscious patient.  Patients  with  conditioned  patterns  of muscle activity may not be able to manipulate the jaw into it, even with assistance by the dentist. In less than 10% of the dentate population the RCP coincides with the ICP. In the remainder the RCP is up to 2 mm or more posterior to the ICP. The term ‘centric relation’ has been used to describe this position, but it has the same disadvantages as the term ‘centric occlusion’ and will not be used. ‘Centric  occlusion’  (CO)  and  ‘centric  relation’ (CR)  are  terms  sometimes  used  in  complete denture  construction  where  they  mean  different  things  to  ICP  and  RCP.

Mandibular movements
Those  patients  who  have  a  discrepancy  between the  RCP  and  ICP  usually  close  straight  into  the ICP from the postural or rest position when the movement is made subconsciously. Patients sitting in  dental  chairs  making  voluntary,  conscious movements  when  asked  to  do  so  by  the  dentist often  make  bizarre  movements  rather  than closing  into  the  ICP  directly. These aberrant movements and contacts are the result of patients trying  too  hard  to  help  and  not  understanding what is required. Students have been heard to ask non-dental  or  medical  patients  to  bite  on  their ‘posterior’  teeth!
However, contact  does  occur  in  the  range between the ICP and RCP during empty swallowing (particularly nocturnal swallowing), during the mastication of a tough bolus and during parafunctional  activity.  Thus the  mandible  can  slide  from the ICP in four main directions with the teeth in contact,  or  in  an  infinite  number  of  directions  at angles  between  these  main  pathways.  The four excursions  are:
• retrusive
• protrusive
• left  lateral
• right  lateral.


Retrusive movements
Movements between the ICP and RCP are usually guided  by  a  limited  number  of  opposing  pairs  of cusps of posterior teeth. The  angle  of  the  slide  between  RCP  and  ICP,  its length  and  the  individual  pairs  of  teeth  that produce it are important and should be examined. Of even greater importance is any unevenness of the movement  producing  bulges  or  lumps  in  the path  of  movement.  These disturbances  to  the smooth movement of the mandible are one form of  occlusal  interference.

Protrusive excursion
In  forward  movement  of  the  mandible  with  the teeth together. It is usually the incisor teeth that guide the movement. This will not be the case in anterior open bites or in Class III incisor relationships. The  angle  and  length  of  movements  will  be determined  by  the  incisor  relationship  so  that,  for example, in a Class II Division II incisor relationship with an increased overbite and reduced overjet, the movement of the mandible has to be almost vertically  downwards  before  it  can  move  forwards. Anterior  guidance  is  important  when  making anterior  crowns  or  bridges.  Sometimes,  when  the teeth are a normal shape, it is helpful to reproduce the  patient’s  existing  guidance  as  accurately  as possible;  on  other  occasions,  for  example,  with worn teeth, it is unnecessary or undesirable to do so,  and  in  fact  the  purpose  of  the  treatment  may be  partly  to  alter  the  incisor  guidance.

Left and right lateral excursions
In lateral excursions the side that the mandible is moving  to  is  known  as  the  working  side  and  the opposite  side  the  non-working  side.  The  term ‘balancing side’ has been used to refer to the non-working  side,  but  since  it  implies  a  balanced occlusion,  balancing  or  stabilizing  a  complete denture  base,  it  should  not  be  used  in  reference to  natural  teeth.
The  contacts  on  the  working  side  are  either between  the  canine  teeth  only  (canine-guided occlusion)  or  between  groups  of teeth on the working side (group function).  Occasionally,  individual  pairs  of posterior teeth will guide the occlusion in lateral excursion,  but  this  is  not  regarded  as  ideal.  The canine-guided  occlusion  is  considered  to  be protective  of  the  posterior  teeth  which  disclude in  lateral  guidance.



Canine guidance 




Group function







Contact  on  the  non-working  side  in  lateral excursions  should  not  normally  occur.  It  does sometimes  occur  after  extractions  and  over-eruption  and  occasionally  following  orthodontic treatment,  particularly  when  this  treatment  has been  carried  out  with  removable  appliances  that have  allowed  the  posterior  teeth  to  tilt. Contact  may  also  occur  in  cases  of posterior  crossbite  where  the  lower  teeth  are placed  buccally  to  the  upper  teeth.

10 Questions and Answers About Dental Radiographic Interpretation

01.  What is the earliest radiographic sign of periapical disease of pulpal origin?
The earliest radiographic sign is widening of the periodontal ligament space around the apex of the tooth.
02 . What is the second most common radiographic sign of periapical disease of pulpal origin?
The second most common radiographic sign is loss of the lamina aura around the apex of the tooth.
03.    Describe the radiographic differences that allow one to distinguish among periapical abscess, granuloma, radicular (periapical) cyst, and an apical surgical scar.
One cannot distinguish among periapical abscess, granuloma, or radicular (periapical) cyst on radiographic grounds alone. All of these lesions are radiolucent with well-defined borders. Whereas an abscess may be expected to be less well corticated than a radicular cyst, this feature is not marked or constant enough to be of real utility. An apical surgical scar may be radiographically distinguishable from the other three lesions if there is radiographic evidence of surgery, such as a retrograde amalgam. Of course, a history should elicit the fact of surgery.
04.    How does the radiographic appearance of pulpal pathology that has extended to in volve the bone differ in primary posterior teeth from the picture commonly seen in perma nent posterior teeth?
In permanent teeth, widening of the periodontal ligament space is seen around the apex of the tooth. In primary teeth, by contrast, the infection presents as widening of the periodontal ligament space or an area of lucency in the furcation area.


05. Does any radiographic sign permit the diagnosis of a nonvital tooth?


It is frequently stated that tooth vitality cannot be determined by radiographs alone, but this is not so. The presence of a root canal filling in a tooth provides virtually conclusive proof of its nonvitality, as does the presence of a retrograde filling, usually amalgam.
06.  At times it may be difficult to distinguish between hypercementosis and condensing or sclerosing osteitis around the apex of a tooth. What radiographic feature permits a definitive diagnosis when one is confronted with this dilemma?
If hypercementosis is present, the periodontal ligament space is visible arou nd the added cementum; that is, the cementum is contained within and is surrounded by the periodontal ligament space. Condensing osteitis, by contrast, is situated outside the periodontal ligament space.
07.  What is the radiographic sign of an ankylosed tooth?
The radiographic sign of an ankylosed tooth is loss of the periodontal ligament space and lamina aura.
08.  What is the earliest radiographic sign of periodontal disease?
The earliest radiographic sign of periodontal disease is loss of density of the crestal cortex, which is best seen in the posterior regions. In the anterior part of the mouth, the alveolar crests lose their pointed appearance and become blunted. In the posterior areas, the alveolar crests usually meet the lamina aura at right angles. In the presence of periodontal disease, these angles become rounded.
09.    What is the earliest radiographic sign of furcation involvement due to periodontal disease? 
In periodontal disease, one may see the loss of a cortical plate, either the buccal or lingual plate, on an intraoral film. The plate may be lost so that the crest now occupies a position apical to the furcation. This appearance, however, does not permit a diagnosis of furcation involvement. Widening of the periodontal ligament space in the furcation area is the earliest radiographic sign of furcation involvement.
10 . What is the radiographic differential diagnosis of a radiolucency on the root of a peri odontally healthy tooth?
Internal resorption, external resorption, and superimposition are the most common causes. Note that the question refers to a periodontally healthy tooth. If bone loss has resulted in exposure of the root, caries and abrasion, among other potential possibilities, enter the picture.

Thursday, July 28, 2011

A Note On Classification, Diagnosis and Management Of Supernumerary Teeth...... with pdf download

Supernumerary teeth may be encountered by the general dental practitioner as a chance finding on a radiograph or as the cause of an impacted central incisor. They may also be found intraorally following spontaneous eruption. The most common supernumerary tooth which appears in the maxillary midline is called a mesiodens. Treatment depends on the type and position of the supernumerary tooth and on its effect on adjacent teeth.

Definition
A supernumerary tooth is one that is additional to the normal series and can be found in almost any region of the dental arch.

Etiology
The etiology of supernumerary teeth is not completely understood.  Various theories exist for the different types of supernumerary. One theory suggests that the supernumerary tooth is created as a result of a dichotomy of the tooth bud. Another theory, well supported in the literature, is the hyper-activity theory, which suggests that supernumeraries are formed as a result of local, independent, conditioned hyperactivity of the dental lamina. Heredity may also play a role in the occurrence of this anomaly, as supernumeraries are more common in the relatives of affected children than in the general population. However, the anomaly does not follow a simple Mendelian pattern.

Prevalence
In a survey of 2,000 schoolchildren, Brook found that supernumerary teeth were present in 0.8% of primary dentitions and in 2.1% of permanent dentitions. Occurrence may be single or multiple, unilateral or bilateral, erupted or impacted, and in one or both jaws. Multiple supernumerary teeth are rare in individuals with no other associated diseases or syndromes. The conditions commonly associated with an increased prevalence of supernumerary teeth include cleft lip and palate, cleidocranial dysplasia (Fig. 1), and Gardner syndrome. Supernumerary teeth associated with cleft lip and palate result from fragmentation of the dental lamina during cleft formation. The frequency of supernumerary permanent teeth in the cleft area in children with unilateral cleft lip or palate or both was found to be 22.2%.5 The frequency of supernumeraries in patients with cleidocranial dysplasia ranged from 22% in the maxillary incisor region to 5% in the molar region.6 While there is no significant sex distribution in primary supernumerary teeth, males are affected approximately twice as frequently as females in the permanent dentition.

Classification
Supernumerary teeth are classified according to morphology and location (Table 1). In the primary dentition, morphology is usually normal or conical. There is a greater variety of forms presenting in the permanent dentition. Four different morphological types of supernumerary teeth have been described:
• conical
• tuberculate
• supplemental
• odontome

Conical
This small peg-shaped conical tooth is the supernumerary most commonly found in the permanent dentition. It develops with root formation ahead of or at an equivalent stage to that of permanent incisors and usually presents as a mesiodens. It may occasionally be found high and inverted into the palate (Fig. 2) or in a horizontal position. In most cases, however, the long axis of the tooth is normally inclined. The conical supernumerary can result in rotation or displacement of the permanent incisor, but rarely delays eruption.

Tuberculate
The tuberculate type of supernumerary possesses more than one cusp or tubercle. It is frequently described as barrel-shaped and may be invaginated. Root formation is delayed compared to that of the permanent incisors. Tuberculate supernumeraries are often paired and are commonly located on the palatal aspect of the central incisors. They rarely erupt and are frequently associ-ated with delayed eruption of the incisors (Figs. 3 and 4).

Supplemental
The supplemental supernumerary refers to a duplication of teeth in the normal series and is found at the end of a tooth series (Fig. 5). The most common supplemental tooth is the permanent maxillary lateral incisor, but supplemental premolars and molars also occur. The majority of supernumeraries found in the primary dentition are of the supplemental type and seldom remain impacted.

Odontoma
Howard lists odontoma as the fourth category of supernumerary tooth. However, this category is not universally accepted. The term “odontoma” refers to any tumor of odontogenic origin. Most authorities, however, accept the view that the odontoma represents a hamartomatous malformation rather than a neoplasm. The lesion is composed of more than one type of tissue and consequently has been called a composite odontoma. Two separate types have been described: the diffuse mass of dental tissue which is totally disorganized is known as a complex composite odontoma  (Fig.  6), whereas the malformation which bears some superficial anatomical similarity to a normal tooth is referred to as a compound composite odontoma.

Problems Associated with Supernumerary Teeth
Failure of Eruption
The presence of a supernumerary tooth is the most common cause for the failure of eruption of a maxillary central incisor. It may also cause retention of the primary incisor. The problem is usually noticed with the eruption of the maxillary lat-eral incisors together with the failure of eruption of one or both central incisors (Figs. 3 and  4). Supernumerary teeth in other locations may also cause failure of eruption of adjacent teeth.

Displacement
The presence of a supernumerary tooth may cause displacement of a permanent tooth. The degree of displacement may vary from a mild rotation to complete displacement. Displacement of the crowns of the incisor teeth is a common feature in the majority of cases associated with delayed eruption.

Crowding
Erupted supplemental teeth most often cause crowding. A supplemental lateral incisor may cause crowding in the upper anterior region. The problem may be resolved by extracting the most displaced or deformed tooth.

Pathology

Dentigerous cyst formation is another problem that may be associated with supernumerary teeth (Fig.  7). Primosch reported an enlarged follicular sac in 30% of cases, but histological evidence of cyst formation was found in only 4 to 9% of cases. Resorption of roots adjacent to a supernumerary may occur but it is extremely rare (Fig. 8).

Alveolar Bone Grafting
Supernumerary teeth may compromise secondary alveolar bone grafting in patients with cleft lip and palate. Erupted supernumeraries are usually removed and the socket site allowed to heal prior to bone grafting. Supernumeraries should not be extracted without consultation with the cleft  team. Cooperation between the general dental practitioner and the cleft team is essential. Unerupted supernumeraries in the cleft site are generally removed at the time of bone grafting.

Implant Site Preparation
The presence of an unerupted supernumerary in a potential implant site may compromise implant placement. The supernumerary may require removal prior to implant placement. If removed at the time of implant placement, bone grafting may be required.

Asymptomatic
Occasionally, supernumerary teeth are not associated with any adverse effects and may be detected as a chance finding during radiographic examination.

Radiographic Examination
A radiographic examination is indicated if abnormal clinical signs are found. An anterior occlusal or periapical radiograph is useful to show the incisor region in detail. The bucco-lingual position of unerupted supernumeraries can be determined using the parallax radiographic principle: the horizontal tube shift method utilizes two periapical radiographs taken with different horizontal tube positions, whereas an occlusal film together with a panorex view are routinely used for vertical parallax. If the supernumerary moves in the same direction as the tube shift it lies in a palatal position, but if it moves in the opposite direction then it lies buccally. Intraoral views may give a misleading impression of the depth of the tooth. A true lateral radiograph of the incisor region assists in locating the supernumeraries that are lying deeply in the palate and enables the practitioner to decide whether a buccal rather than a palatal approach should be used to remove them.

Management of Supernumeraries
Treatment depends on the type and position of the supernumerary tooth and on its effect or potential effect on adjacent teeth. The management of a supernumerary tooth should form part of a comprehensive treatment plan and should not be considered in isolation.

Indications for Supernumerary Removal
Removal of the supernumerary tooth is recommended  where:
• central incisor eruption has been delayed or inhibited;
• altered eruption or displacement of central incisors is evident;
• there is associated pathology;
• active orthodontic alignment of an incisor in close proximity to the supernumerary is envisaged;
• its presence would compromise secondary alveolar bone grafting in cleft lip and palate patients;
• the tooth is present in bone designated for implant placement;
• spontaneous eruption of the supernumerary has occurred.
Indications for Monitoring Without Supernumerary Removal
Extraction is not always the treatment of choice for supernumerary teeth. They may be monitored without removal where:
• satisfactory eruption of related teeth has occurred;
• no active orthodontic treatment is envisaged;
• there is no associated pathology;
• removal would prejudice the vitality of the related teeth.

Recommendations Following Supernumerary Removal
Three factors influence the time it takes for an impacted tooth to erupt following removal of the supernumerary:
• the type of supernumerary tooth;
• the distance the unerupted permanent tooth was displaced;
• the space available within the arch for the unerupted tooth.
Removal of a supernumerary tooth preventing permanent tooth eruption usually results in the eruption of the tooth, provided adequate space is available in the arch to accommodate it. Di Biase found 75% of incisors erupted spontaneously after removal of the supernumerary. Eruption occurred on average within  months, provided that the incisor was not too far displaced and that sufficient space was available.
Although the majority of authors recommend exposure of the unerupted tooth when the supernumerary is removed, Di Biase advocates conservative management without exposure.
A lower spontaneous eruption rate of 54% following supernumerary removal was reported by Witsenburg and Boering, who recommend the routine bonding of an attachment and gold chain for orthodontic traction at the time of surgery. However, the time and expense involved in this technique may not be justified if the rates of spontaneous incisor eruption are found to be in the region of 75 to 78%, as reported by both Di Biase and Mitchell and Bennett.
If there is adequate space in the arch for the unerupted incisor following supernumerary removal, space maintenance can be ensured by fitting a simple removable appliance. If the space is inadequate, the adjacent teeth will need to be moved distally to create space for incisor eruption. In that case, the primary canines may need to be extracted at the same time as the supernumerary tooth. Where there is adequate space and the incisor tooth fails to erupt, surgical exposure of the incisor and orthodontic traction is usually required.


                  ........Download PDF Note........

Wednesday, July 27, 2011

A Note On Types Of Ceramic Crowns Used For Anterior Crown Restorations

Anterior complete crowns for vital teeth
In  the  anterior  part  of  the  mouth  appearance  is of  overriding  importance,  and  so  the  only  types of  crown  to  be  considered  are  those  with  a tooth-coloured labial or buccal surface. These fall into  three  groups:
• Ceramic  crowns
• Metal–ceramic  crowns
• Other  types  of  crowns.
Ceramic  crowns

In  recent  years  there  have  been  several  developments in the ceramics used for crowns. These can be  classified  as:
• Traditional  fused  porcelain  jacket  crowns(PJCs)
• Pressed  ceramic  crowns
• Milled  ceramic  crowns
• Cast  crowns
• Reinforced  crowns
• Ceramic  resin  bonded  crowns.

Traditional porcelain jacket crowns (PJCs)
This  is  the  oldest  type  of  tooth-coloured  crown and  has  been  in  use  for  more  than  a  century.  It consists  of  a  more  or  less  even  layer  of  porcelain,  usually  between  1  and  2 mm  thick,  covering the  entire  tooth. Following Figures  show  a selection of traditional feldspathic porcelain jacket crowns  in  place.
The  traditional  feldspathic  PJC  is  made  by adapting  a  very  thin  platinum  foil  to  a  die  made from  an  impression  of  the  prepared  tooth. Porcelain  powder,  mixed  with  water  or  a  special fluid,  is  built  onto  the  platinum  foil  and  fired  in the  furnace.  All  PJCs  made  in  this  way  are  now strengthened by having alumina incorporated into the  porcelain  powder.  A  core  of  high-alumina porcelain is fired onto the platinum foil. This high-alumina  core  is  opaque  and  needs  to  be  covered by  more  translucent  porcelain  that  contains  less alumina.
Variations  on  fused  ceramic  crowns  have  been developed  but  most  have  now  been  replaced  by the  systems  described  later.  Examples  of  these strengthened  ceramic  systems  were  Hi-Ceram and  In-Ceram.

Strengthened  porcelain  crowns  (Hi-Ceram)  on  both central  incisor  teeth












The  upper  left  lateral  incisor  tooth  has  been
moved  orthodontically  into  the  position  of  the  central incisor  and  crowned  with  an  infiltrated,  reinforced system  (Inceram)  to  resemble  the  missing  central incisor







An  alternative  approach  is  to  fire  an  extra-strong  core  of  ceramic  material  to  a  refractory die  and  then  add  further  layers  of  conventional feldspathic  porcelain.  Once  finished,  the  refractory  die  is  grit-blasted  away,  leaving  a  fitting surface  that  is  slightly  rough,  aiding  retention. Both these  systems  can  also  be  used  to  make porcelain  veneers.
Conventional  dental  porcelain  is  physically more  like  glass  than  the  porcelain  used  for domestic  purposes.  It  is  relatively  brittle,  and before  a  PJC  is  cemented  it  can  be  broken  fairly easily.  However,  once  it  is  cemented  and supported  by  the  dentine  of  the  tooth,  the  force required  to  fracture  it  is  of  the  same  order  of magnitude  as  the  force  required  to  fracture  the enamel  of  a  natural  tooth.
However,  traditional  PJCs  do  fracture  and  so the  other  systems  have  all  been  developed  to produce  stronger  all-ceramic  crowns.

Pressed ceramic crowns
There  are  a  number  of  systems  used  to  produce a  strong  ceramic  core  by  pressing  a  ceramic material at high temperature and pressure onto a die  and  then  building  up  layers  of  traditional porcelain  to  create  the  right  contour  and  shade. Examples  of  crowns  made  by  this  process  are shown bellow.



Equipment  for  construction  of  an  Empress  crown













Pressed crowns on the upper and lower incisor teeth 
in a patient with mild amelogenesis imperfecta. This can 

be seen on the uncrowned teeth, particularly the lower 

right  first  premolar.  The  system  used  was  Empress




Laboratory milled cores and crowns
Several  computer  aided  designs/computer  aided manufacture  (CAD-CAM)  have  been  developed and  more  are  in  the  pipeline.  One  example  is  a technique  by  which  the  die  is  scanned  in  a computer  and  the  digital  record  is  sent  electronically  to  a  central  laboratory,  often  in  another country,  where  a  core  is  produced  in  a  strong ceramic  material.  This  is  then  returned  to  the original  laboratory  where  additional  porcelain  is added  to  complete  the  crown.  The system  can also  mill  metal,  in  particular  titanium  (Procera). The computer equipment is shown in Figure 2.2d and  crowns  made  by  this  process  are  shown  in Figure  2.2e  and  f.


















The scanner used in the process of making a Procera
crown







A  Procera  core  of  dense  aluminous  porcelain  ready.The  porcelain  will  be  fired  directly  onto  this.






Procera  crowns  restoring  three  incisor  teeth. Note how the crowns disguise the gold post and cores so  the  appearance  is  the  same  as  the  crown  on  the
natural  tooth






Zirconia cores
Porcelain  crowns  can  also  be  manufactured  using complex  laboratory  techniques  with  a  zirconia core  onto  which  conventional  porcelain  is  built. Zirconia  is  an  extremely  strong  material  comparable  to  metal  and  is  dense  white  in  appearance. The conventional porcelain therefore needs to be relatively  thick  for  the  translucent  porcelain  to mask  the  opaque  core  underneath.  Zirconia-based crowns are proposed by the manufacturers for use on posterior as well as anterior teeth due to  their  great  potential  strength,  but  there  is  not yet  sufficient  evidence  that  they  will  survive  for the  long  term  in  high  stress  situations.

Chair-side milled restorations
Chair-side milling  systems  have  been  in  development  for  some  years.  Although  these  systems  do not  yet  produce  reliable  crowns  it  is  anticipated that  they  will  do  so  in  the  foreseeable  future.

Cast ceramic systems
One  of  the  earliest  developments  in  the  1970s was  of  a  system  to  produce  strong  ceramic crowns  by  the  Dicor  process  in  which  a  wax pattern of the crown was made on a conventional die,  invested  and  cast  in  a  glass/ceramic  material. The casting was then placed in a ceramming oven for several hours, during which it went through a crystallization conversion  and  became  much stronger.  At  this  stage  the  casting  had  a  cloudy-clear  appearance  (similar  to  frosted  glass).  It was then stained and characterized using conventional feldspathic  porcelains  in  a  porcelain  furnace. Although the commercially available Dicor system was  developed  by  the  same  company  that  devel-oped  domestic  Pyrex  glassware,  the  manufacturers  state  that  the  material  is  not  the  same  as Pyrex. A number of other castable ceramic or hot transfer-moulded  glass  ceramic  systems  have been  developed.


A  cast  ceramic  crown  (Dicor)  on  the  upper  right central  incisor






Reinforced porcelains
One technique is to form an alumina substructure on  a  special  plaster  die  and  following  sintering  in a  furnace  the  porous  substructure  is  coated  with glass  fired  powder  and  further  fired  for  several hours.  This  infiltrates  the  pores  and  eliminates them  as  a  source  of  weakness.  Filling  the  pores also  improves  translucency  and  the  final  appearance when additional porcelain is added.

Thin ceramic resin bonded crowns


Peg-shaped lateral incisors.






The upper right lateral incisor prepared for a resin bonded  ceramic  crown.  The  preparation  is  entirely within  enamel.  The  neck  of  the  tooth  has  been prepared all round with a chamfer finishing line, similar to the preparation for a veneer, and a small amount has been removed from the incisal edge. Nothing has been  removed  from  the  labial  or  proximal  surfaces other than blending them into the gingival finishing line.



Palatal view of the finished crowns.






The labial appearance.



All the previous  crowns  are  usually  cemented  by conventional  means.  However,  a conservative  technique  is  to  prepare  the  tooth within  enamel  exposing  the  minimum  amount  of dentine and then making thin ceramic crowns, no thicker  than  a  porcelain  veneer  but covering the whole tooth. This is then bonded by etching  the  enamel  surface,  grit-blasting  the  fit surface  of  the  crown  and  bonding  with  an adhesive  resin  material. These restorations  are  becoming  more  popular  with some  dentists,  who  believe  that  their  prognosis may be better than ceramic veneers because they go  right  round  the  tooth,  thereby  reducing  the effects  of  the  difference  in  thermal  expansion between  porcelain  and  enamel,  and  also  the  risk of  marginal  leakage  and  staining  is  reduced.

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