Diagnosis and Treatment Planning for Multiple Implants in Esthetic Zone

Abstract

A new era in dentistry dawned when successfully osseointegrated implants were used to restore edentulous jaws by Branemark et al. This important discovery opened up avenues previously unimaginable in edentulous rehabilitation. The predictability and longevity of implant restoration have been irrevocably cemented in dentistry. Even with state-of-the-art technologies for implant planning and placement, the rehabilitation of the anterior maxilla has posed a particular problem because of the high esthetic demand and complex anatomy of the region. Since these two parameters vary highly in patients, a careful evaluation of the clinical scenario and comprehensive history-taking should precede meticulous treatment planning to ensure accurate diagnosis and successful treatment outcomes. Both fixed and removable options are available for the rehabilitation of the edentulous anterior maxilla. This chapter aims to compare these options and prosthetic designs with an emphasis on diagnosis and treatment planning. A comprehensive checklist for easy decision-making regarding treatment planning will be presented.

1. Introduction

‘One of the most dangerous diseases is diagnosis’.

- George Bernard Shaw

Successful rehabilitation of partially edentulous arch by means of osseointegrated implants was popularized by Branemark et al. [1, 2, 3]. This launched a new era of management for the partially edentulous predicament. The rehabilitation of anterior maxillary teeth to date remains one of the most challenging situations in dentistry due to a number of esthetic and functional aspects of the restoration [2, 3, 4]. Both fixed and removable implant-supported prosthesis are used to treat this condition. High esthetic demand coupled with exacting patient expectations deems it necessary to invest considerable time in accurate diagnosis and treatment planning. This would ensure predictable outcomes and patient satisfaction. This chapter aims to compare available treatment options and prosthesis design for edentulous maxilla with emphasis on diagnosis and treatment planning. This would be accomplished through an evidence-based review of factors influencing the clinical decision-making process. Criteria for decision-making parameters with regard to removable v/s fixed prosthesis will also be put in place.

2. Special condition in maxilla

Historically the use and research of implant prosthesis were conducted predominantly on the mandibular arch, due to reduced denture-bearing surface and function of the tongue contributing to the instability of mandibular dentures. A multitude of designs was evaluated from implant-supported complete dentures to subperiosteal implants to provide better patient stability and comfort [5].

The accommodation to maxillary denture was easier than the mandibular counterpart, in part due to better retention, stability, support, and esthetics. When implant rehabilitation was attempted, the principles established for mandibular implants were adopted. This meant screw-retained cantilever pontics were fabricated in spaces with excessive resorption and long standard abutments were installed with prosthesis on top. Though acceptable in the mandible, in the maxilla it left open interproximal spaces compromising esthetics [5].

This is complicated by factors like (1) the resorption pattern of the maxilla, where following extraction the horizontal bone resorption is twice as pronounced as vertical (2) anatomical limitation for implant placement due to the vertical distance between the alveolar crest and the nasal sinuses in the anterior maxilla and (3) pneumatization of maxillary sinuses which limits implant placement in posteriors [6]. The long-term prognosis for implants in the maxilla is less secure than that of the edentulous mandible. The poor bone quantity, quality, and high esthetic demands complicate diagnosis, treatment planning, and treatment in the anterior maxillary region [7].

3. Diagnosis

The most important decision to be made while rehabilitating an edentulous maxilla is whether to restore it with a fixed or removable prosthesis. All diagnostic criteria must be evaluated before formulating a treatment plan. Parameters such as bone quality and quantity, lip support, lip line and esthetic demands, etc., to be evaluated are described in detail by Zitzmann and Marinello [8] implant placement should be deferred until a definitive diagnosis and treatment plan have been framed.

Checklist for implant rehabilitation:

1. Patient factors

   1. Patient preference

   2. Phonation

   3. Ability to effectively perform oral hygiene

   4. Economics

2. Extra oral examination [9]

   1. Facial and lip support

   2. Esthetic plane

   3. Maxillomandibular relationship

   4. Smile line

   5. Lip length

   6. Vestibular space

   7. Horizontal tooth display

3. Intraoral examination

   1. Quality of mucosa

   2. Thickness of mucosa

   3. Quantity and quality of available bone

   4. Incisal papilla position

   5. Interarch space

   6. Speech disruption

   7. Tooth size to arch size discrepancies

3.1 Patient factors

If the patient presents with an existing denture, it could act as one of the best diagnostic tools. The denture must be examined thoroughly objectively for retention, support, stability, vertical dimension, the tooth selection and arrangement, phonetics and esthetics. Patients option on the same should also be carefully noted down.

Tendency to prefer fixed restorations over removable have been demonstrated previously, but the responsibility of determining the best treatment option lies with the restorative dentist after careful evaluation of all the parameters [8].

3.2 Extra-oral examination

3.2.1 Facial and lip support

The resorption pattern of maxilla generally proceeds in a cranial and medial fashion, rendering a retruded position of maxilla in anterior region. Assessment must be done with and without the existing denture from both front and profile view. Inadequate facial support may be corrected by buccal flange of removable restoration. Lip support is provided by shape of alveolar ridge and cervical crown contour of the anterior teeth (Figure 1).

Figure 1.

Extraoral and intraoral factors.

A diagnostic set up must be prepared to better evaluate anterior teeth, position and relation to lip. Often depending on the severity of the resorption, there may be discrepancy between the anticipated position of teeth and the ridge. This must be considered while planning the implant position as so to satisfy patient expectation of function, esthetics and phonation. Which trying to overcome larger discrepancies, extensive grafting and removable prosthesis with flange may be of use, the associated limitations and risks must be clearly explained to the patient [9].

3.2.2 Esthetic plane and maxillomandibular relationship

“E” plane represents a line drawn from the nose tip to the chin tip. For a pleasing appearance the upper lip and lower lip must be 4 m and 2 mm behind the line respectively. There are mild changes amongst ethnic groups. It may be generalized that closer the lips are to the “E” plane the more dominate the teeth and lips will appear, the farther behind the “E” plane the lips are, the more dominate the nose and chin appear.

Based on this for a patient with Class 2 maxillomandibular relationship, where maxilla is prognathic, having convex profile care must be taken not to anterior teeth large or too white as to make them further dominant. And vice-verse should be considered for a concave profile patient, having Class 3 maxillomandibular relationship, where the mandible is prognathic. Lighter shades may benefit these patients by balancing the stronger nose and chin [9].

3.2.3 Smile line and lip length

The orofacial muscular tonicity and lip mobility during speech and smile determines the smile line. An average smile as described by Tjan et al. displays 75–100% of maxillary incisors and interproximal gingiva. Low smile line displays less than 75% of the incisors, and high smile displays additional gingiva [9, 10]. Vig and Brundo classified patients into 5 groups based on upper lip length and presented the corresponding tooth display [11]. They concluded that average lip length of 21–25 mm displayed 2.18 mm and 1 mm of maxillary and mandibular teeth. Short lip length of 10–15 mm exposed 4 mm of maxillary teeth and 0.7 mm of mandibular teeth. Whereas long lip length of 31–35 mm showed only 0.25 mm maxillary incisor and 2.25 mm of mandibular incisors.

Ridge display during smile presents a challenge in rehabilitation as gingiva- restoration junction would be in visible zone. Lip and support must be evaluated as they influence the tooth exposure during smile and speech. A long lip in most instances covers the anterior reducing the exposure during smile, favorable for rehabilitation of anterior. Whereas a short lip exposes anterior and meticulous planning with be required to satisfy esthetic parameters.

3.2.4 Vestibular space and horizontal tooth display

When a patient presents with an existing denture, the smile must be evaluated with and without the denture. The movement of lips and display zone of smile must be noted. The lips function as curtains than frame the teeth during smile. Smile esthetics is affected by the amount of tooth and soft tissue displayed both in vertical and horizontal dimension. Assessment must be made include posed/voluntary smile which is static and an involuntary or dynamic smile. The lip is often much more animated in an involuntary smile. Excessive display or gummy smile is less attractive and often challenging to rehabilitate as the junction between the prosthesis and the soft tissue may be in the smile zone and discernable. Use of removable prosthesis in such cases with pink acrylic seamlessly forming a scaffolding of interdental papilla and attached gingival would be much preferred [12].

Frush and Fischer described buccal corridor space as the space between the buccal surfaces of posterior teeth and corners of the mouth in smile. This negative space has influence on smile esthetics as well. The presence of this space creates a much more natural smile as opposed to denture like smile created by elimination of the space all together. It is suggested that a minimal buccal corridor space is more attractive [13, 14].

3.3 Intra-oral examination

3.3.1 Quality and quantity of mucosa

Loss of tooth is accompanied with the resorption of interseptal bone, and bone remodeling around the socket. Often the interdental papilla is flattened or is missing due to lack of interproximal contact. The loss of interdental papilla in most scenario is an irreversible damage [15]. Achieving pre-extraction papillary architecture is unlikely and the patient must be made acutely aware of this.

The quality of mucosa should be evaluated by palpation, radiographs and sounding [16]. Gingival biotype was classified by Seibert and Lindhe as thick, thickness of more than or equal to 2 mm and thin, having thickness less than 1.5 mm [17]. Thin gingival biotype presents consider challenge in molding and thoughts must be directed towards soft tissue grafting to change the biotype to thick. Thick biotype is easier to mold and helps hide the abutment margins and facilitates proper emergence of the prosthetic crown.

The loss of interdental papilla may be compensated by manipulating the soft tissues by the use of ovate pontic. Or by the use of gingival colored porcelain or acrylic resin.

3.3.2 Bone quality and quantity

The resorption in maxilla follows a centripetal pattern. In severe resorption cases this results in maxilla which is superior and palatal to the original position of the dentate alveolar ridge. This creates a biomechanical disadvantage while placing anterior implant where prosthesis must most definitely be placed in pre-extraction tooth position with a labial cantilever. This also poses a problem in posterior region where the ridge may be in cross bite condition. This would result in prosthesis in cross bite or with excessive facial cantilever. Hence a sound assessment of the bone quality and quantity should precede any treatment planning [18].

A classification based on post extraction ridge changes of mandible was proposed by Atwood [19], though quantitative, lacking enough details to help in detailed treatment planning, lead to classification by Lekholm and Zarb to be popularized [5]. Both maxilla and mandible was classified into 5 shapes (A–E) based on the degree of resorption and 4 patterns (1–4) based on quantity and type of cortical bone present. Shape A represents minimal resorption and E severe resorption, type 1 having thick cortical area and type 4 thinnest. The Quality of bone often dictates the treatment planning. Edentulous maxilla generally comprises of type 3 or 4 bone quality, may prescribe placement of additional implants, in anticipation of failure of one or more. Another A Therapeutically Oriented Classification- HVC Ridge Deficiency Classification delivers therapeutic recommendations for both hard and soft tissue deficiencies [20].

As visual inspection cannot reveal the density, and volume of the bone underneath the soft tissue, radiographical examination is mandatory. Cone beam computer tomography (CBCT) reveal three-dimensional architecture for precise planning of surgical and prosthetic phases. The CBCT may be performed with gutta percha or metal markers for maximum advantage from the scan. These markers are placed perpendicular to the occlusal plane in acrylic resin duplicates of diagnostic denture. The exact trajectory of the bone can be evaluated using CBCT making treatment planning easier and unfailing [21].

Long standing edentulism of posterior maxilla may result in pneumatization of maxillary sinuses, reducing the quantity if bone available for implant placement in this region. Corrective procedure like maxillary sinus lift and ridge augmentation can be performed [22]. The donor site for the augmentation mostly likely depends on the volume of bone required. Commonly utilized site is iliac crest when augmenting both sinuses, requiring additional surgical procedure and less acceptance amongst patients. Alternatively, information from the CBCT may be used to direct the implant away to alternative sites with voluminous bone making the procedure minimally invasive [23]. Zygomatic, maxillary tuberosity and pterygomaxillary implants can be used as an alternative treatment option. Zygomatic implants engage the zygomatic bone inferolateral to the orbital rim, along with anterior implants they can provide anchorage to maxillary prosthesis.

3.3.3 Incisal papilla position

Anterior maxillary implant placement is further complicated due to the anatomical variations in dimension of incisive canal and foramen. The canal has two openings—the incisive foramen and nasopalatine foramen. The nasopalatine nerves and vessels transverse the canal. Accidental damage to this anatomical structure may cause nervous tissue injury, sensory dysfunction and even non osseointegration of implants. The size, position, shape and number of foramina are varied in population. The presence of wider foramina along with thin alveolar bone may require surgical intervention (Figure 1). Careful clinical and radiographic assessment assisted by CBCT must be made [8].

3.3.4 Inter arch space

Available interarch space commands the prosthetic design. Different designs, different types of prosthesis require different dimensional tolerance. The resorption pattern of alveolar ridge has been a considerable problem. Accurately mounted casts on semi-adjustable articular with facebow transfer can be used to study the interarch distance and make decisions regarding the prosthetic design type best situated for the situation (Figure 1).

A conventional overdenture requires 12–16 mm, of which 2–3 mm is reserved for the heat cure acrylic resin to provide sufficient bulk, and rest for the prosthetic teeth. When it is planned to connect, he implants additional 2–3 mm space is required to accommodate he superstructures. A screw retained prosthesis requires only 10–12 mm space limitations may require reestablishing patient’s vertical dimension or change to occlusal plane [24].

3.3.5 Incisal edge position

Guidelines used in conventional complete denture construction can be used to determine the incisal edge position of the future prosthesis. Visibility of 2 mm anteriorly determines the anterior occlusal plane. Additionally, ‘F’, ‘V’ and ‘S’ sounds can be used to determine the correct vertical and horizontal placement of the incisors [25]. The average length of central incisor is 10.5 mm, clinical crown height may increase in elderly due to gingival recession. The in clinical of the anterior teeth should be determined based on the lip support required. After determining the crown height and angulation the available space from the crestal bone height should be calculated (Figure 1).

In case of minimal resorption, the cervical edge of the anterior teeth would coincide with the crestal soft tissue level, in which case a fixed restoration would be ideal. A try- in should be done without the flange of the aid in this assessment. In case of large discrepancy between the crest and cervical aspect of try teeth, but lip support, pink ceramic can be used to overcome this discrepancy. To optimize the existence of both vertical and horizontal discrepancies removable prosthesis with flange may be indicated [25].

4. Radiographic diagnosis

As mentioned earlier the accurate assessment of bone quality and quantity is paramount for successful implant treatment. It affects implant selection, position and angulation. A CBCT with a radiographic stent or diagnostic set up with radiographic markers incorporated depicting the ideal implant position can be used. The incisal edge of the radiographic marker represents the ideal position of the screw access channel of a screw retained fixed implant prosthesis located at the cingulum or the central fossa. All possible implant positions are marked with titanium pins (7 mm in length) after determining the ideal angulation using a surveyor. The markers should be incorporated so as to be perpendicular to the occlusal plane and end apically at the height of the planned clinical crown margin [24].

5. Treatment planning

A foolproof treatment plan should be devised after careful consideration of patient needs and expectations, and all the diagnostic findings addressed above. It is paramount that the treatment plan addresses the chief complaint of the patient. The expected final outcome should be communicated with the patient with utmost clarity. To avoid disappointment after undergoing an expensive and time-consuming treatment patient education, informed consent after understanding and acknowledging the advantages, disadvantages and limitations of the plan is vital. Also, any expected modifications to the plan should be explained and signed off by the patient prior to the treatment [12].

Jivraj, Chee and Corrado have listed the factors to be considered in treatment planning for edentulous maxilla:

1. Esthetics and patient desires

2. Type of prosthesis

3. Number of implants

4. Implant distribution

5. Economics

5.1 Esthetic and patient desire

Understanding the patient’s motivation for seeking treatment is integral to the satisfying these needs. Promises must not be made before thorough diagnosis. in case a demand to replace a removable prosthesis with fixed is made by the patient, consequence of missing denture flange must be explained to the patient. The flange may compensate the lip to teeth horizontal discrepancy, or vertical discrepancy of brought about because of severe resorption. In such cases a complete denture provides better esthetics by reproducing the lost soft tissue especially interdental papilla in pink acrylic. This may be lost entirely when replacing with a fixed prosthesis, and patient may end up with unesthetic black triangles, due to missing interdental papilla in the esthetic zone. An effort can be made to create an illusion of interdental papilla by altering the contact point between the teeth and staining, or utilizing pink ceramics, the results may or may not be to the satisfaction of the patient. This must be communicated with the patient explicitly [12].

5.2 Type of prosthesis

Implant prosthesis may derive support either from the underlying implant alone or from both the implant and foundation tissues. Implant prosthesis can be categorized as fixed or removable. Fixed prosthesis is metal ceramic prosthesis that are supported by the underlying implants and based on the discrepancy between the planned tooth position and the crest of the soft tissue may or may not require pink ceramic to simulate gingival contour. Removable prostheses are categorized as implant supported overdentures and implant retained overdentures [24]. An implant retained prosthesis is supported by foundation tissues and retained by the implant through ball or magnets attachments, bar and clips or precision milled components [12].

5.3 Number of implants

Consideration must be giving to a multitude of factors when planning the number of implants to be placed, some of them are:

1. Quality of bone

2. Anticipated force to be placed on the restoration

3. Relationship between the shape of the residual ridge and the dental arch form.

5.3.1 Quality of bone

Success of implant rehabilitation in maxilla is less than mandible. Recommendations for rehabilitation edentulous maxilla with fixed prosthesis is to place 6–8 implants at a distance of 10–15 mm, and with removable restoration 4–6 implants for both implant and implant and tissue supported restoration [24]. Maxilla is frequently composed of type 3 or 4 quality bone. When the quality of the bone is too poor for conventional drill, over engineering of the maxilla may be called for.

Long term edentulism in posterior maxilla leading to pneumatization of sinuses and refusal to ridge augmentation procedures, may drive the restorative dentist to consider either cantilever restorations or short dental arch concept [26, 27].

5.3.2 Anticipated forces

Facial and oral muscle tonicity must be taken int. o consideration when planning implant prosthesis. Any hypertrophy of oral musculature must be noted, especially of the masseter. Pronounced antegonial notch indicative of bruxer and likely high forces on the restoration must be anticipated. An over engineering would be advised in such cases.

The opposing arch must be carefully examined for anticipated occlusal contacts, presence of restoration or prosthesis. A rehabilitation opposing natural dentition is much likely to exert larger force than one opposing a complete denture. Larger the anticipated force more the number of implants should be allowed for [12].

5.3.3 Relationship between shape of residual ridge and dental arch form

Dental arches and the residual ridge are classified as ovoid, square and tapering. An esthetic rehabilitation may require the restored dental arch form to deviate from the residual ridge shape. The arch form is determined by the last tooth on the pre maxilla and not the residual ridge form, which may in cases have to be placed facially to attain better esthetics.

An ovoid dental arch requires placement of one implant each at the canine position and at least one additional implant, preferably in the central incisor position. The premaxilla to accommodate 3 implants may have to undergo augmentation procedures. The addition of the anterior implant in the central incisor position provides better resistance to forces and provides biomechanical stability to the prostheses design. This reduces the forces on the abutment screw, reducing the chances of screw loosening. In a square arch the canine, lateral and central incisor are placed more or less on the same plane. This reduces the forces between the cantilevered lateral and central incisors, and placement of one implant each at canine region may suffice when splinted with posterior implants to restore the square arch [12].

Rehabilitating a tapered arch is the most challenging situation, as the anterior implants witness the greatest forces, because the anterior teeth are cantilevered far facially. This dictates placement of four implants in the premaxilla to replace the six missing anterior teeth.

5.4 Implant distribution

Implant distribution and placement will be the determining factor in restoration’s emergence profile. Patients planned to receive removable or fixed restoration with considerable gingival ceramic can be forgiving to incorrect or placement of implants in interproximal position. The flange or pink porcelain will disguise the improper placement. For rehabilitation with fixed prosthesis, it is imperative that implant placement be precisely planned and executed using surgical guides. Incorrect placement or placement in interproximal position causes esthetic and hygiene maintenance problems [4].

The distribution of implant along the arch is crucial for better load sharing. Antero posterior spread of the implant should be optimized and cantilever minimized. Splinting advantageous as it improves biomechanics of the prosthesis design. In case of implant retained prosthesis the placement becomes crucial as straight-line placement would be required to successfully execute a connection for a bar, that does not impinge the palatal tissues. The distribution should be as to accommodate a clip to be placed in the denture [24].

5.5 Economics

Implant rehabilitation is a costly affair, and both fabrication and maintenance phase should be taken into account. Fixed restoration requires implant components and meticulous laboratory support and are hence costlier than their removable counterpart. Though the maintenance phase requires less investment. While overdentures fabrication is cheaper, the maintenance is consistent, and hence it is questionable whether the economical indication of overdenture be justified. The cost factor of both phases must be made aware to the patient [12].

Table 1 summarizes the checklist to be followed for treatment planning in edentulous maxilla for implant prosthesis.

Checklist for implant rehabilitation:
	Fixed implant prosthesis	Removable implant prosthesis
1. Patient factors
a. Patient preference	Most preferred	With minimal palatal coverage is preferred
b. Phonation	Most problems	Fewer problems
c. Ability to effectively perform oral hygiene	Most demanding	Easier
d. Economics	More expensive initially	Less expensive initially
2. Extra oral examination
a. Facial and lip support	Present	Needed from the prosthesis
b. Esthetic plane	Convex profile	Concave profile
c. Maxillomandibular relationship	Angle class I/ II	Angle class III
d. Smile line	Low	High
e. Lip length	Long	Short
f. Vestibular space	Less visible	Increased visibility
g. Horizontal tooth display	Minimal	Maximum
3. Intraoral examination
a. Quality of mucosa	Keratinized	Non keratinized
b. Thickness of mucosa	Thick	Thin
c. Quantity and quality of available bone	Shape A/B Type 2/3	Shape C/D/E Type 3/4
d. Incisal papilla position	Palatal	Crestal/buccal
e. Interarch space	10–12 mm	>12 mm
f. Tooth size to arch size discrepancies	Absent	Present

Table 1.

Checklist to be followed for treatment planning in edentulous maxilla for implant prosthesis.

6. Conclusion

Diagnosis and treatment planning is a crucial step in rehabilitation of edentulous maxilla with implant supported or retained prosthesis. A myriad of factors affects the type of prosthesis design, implant number and distribution. Factors to consider before making a final treatment plan include parameters such as patient related factors like expectation and desire, extraoral factors like facial and lip support, smile line, and intraoral factors such as bone and soft tissue quality and quantity. And all these must be carefully considered, clinical and radiographic evaluation is must be done with at most sincerity and a treatment plan conceived must a line with patient expectation.