ARTÍCULO ESPECIAL

 

Management of anteroposterior bone defects in aesthetic restoration of the front teeth

Manejo de defectos óseos anteroposteriores en el frente estético

 

 

 

J. Caubet Biayna¹, I. Heras Rincón², J. Sánchez Mayoral¹, M. Morey Mas³, J.I. Iriarte Ortabe⁴

1 Cirujano Oral y Maxilofacial Práctica privada GBCOM. Palma de Mallorca. España.
2 Médico Residente. Servicio de Cirugía Oral y Maxilofacial. Hospital 12 Octubre Madrid. España
3 Médico adjunto. Servicio de COMF. Hospital Universitario Son Dureta. P. de Mallorca. España.
4 Jefe Servicio de COMF. Hospital Universitario Son Dureta. P. de Mallorca. España.

Correspondence

 

 

 

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ABSTRACT

Objective: Development of a clinical protocol for the management of anteroposterior bone defects in the front teeth followed by later rehabilitation with osseointegrated implants.
Material and method: The anatomic concepts that characterize the front teeth and the placement and three-dimensional relations of implants were reviewed. Recent literature on bone and soft-tissue reconstruction techniques for the front teeth was reviewed. We present our 8-year experience in managing these defects with different types of grafts.
Results: A protocol for the treatment of bone defects for rehabilitation of the front teeth with osseointegrated implants is described that depends on the magnitude of the bone defect (small defects that do not jeopardize implant placement, single-wall defects that jeopardize implant placement, or two or three-wall defects) and the patient’s periodontal biotype.
Conclusions: In aesthetic restoration, maximum precautions must be taken in placing any implant. These precautions must be even greater when bone grafts are required. Proper bone graft management makes it possible to correctly place the implants threedimensionally to achieve acceptable aesthetic results for restorations.

Key words: Aesthetic; Zone; Graft; Defect; Bone.

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RESUMEN

Objetivo: Desarrollar un protocolo clínico para el manejo de defectos óseos anteroposteriores en el frente estético para la posterior rehabilitación con implantes osteointegrados.
Material y método: Repasamos conceptos anatómicos que caracterizan el frente estético, de colocación y relación tridimensional de los implantes y hacemos una revisión bibliográfica actualizada sobre las distintas técnicas reconstructivas óseas y de partes blandas centradas en el frente estético. Recogemos nuestra experiencia tras 8 años de manejo con distintos tipos de injertos en el manejo de estos defectos.
Resultados: En función de la magnitud del defecto óseo (pequeño que no compromete la colocación del implante, de una pared que compromete la colocación del implante o de dos o tres paredes) y del biotipo periodontal del paciente exponemos un protocolo de tratamiento de defectos óseos para la rehabilitación con implantes osteointegrados en el frente estético.
Conclusiones: En el sector estético deben tomarse las máximas precauciones en la colocación de cualquier implante. Estas precauciones deben ser aún mayores en los casos de injertos óseos. El adecuado manejo de los injertos óseos nos permitirá colocar los implantes de modo tridimensional correcto para conseguir resultados estéticos en las restauraciones.

Palabras clave: Estética; Zona; Injerto; Defecto; Óseo.

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Introduction

Bone loss is a problem that makes it difficult or impossible to place implants. In this article we will discuss the management of bone defects in aesthetic reconstruction for the placement of osseointegrated implants. There are many causes of bone loss, but a simple extraction and the use of dental prostheses can increase bone resorption, causing large deformities. In these areas, the objective is not only the osseointegration of the implant. The final outcome has to be an implantsupported restoration surrounded by good quality bone and soft tissues that harmonize with the existing dentition. In order to achieve predictable aesthetic results, we need to know all the factors that can influence outcome. An error in soft tissue management or implant position, despite the sufficiency of the bone and soft tissues, can lead to aesthetic failure. For that reason we will:

• Analyze the anatomic concepts before beginning treatment,

• Review different bone reconstruction techniques,

• Develop a clinical protocol for the aesthetic management of bone defects,

• Illustrate the management of each type of bone defect with a clinical case.

 

Anatomic concepts in aesthetic restoration of the front teeth

Smile line

The study of the smile line is the most important element in evaluating the patient’s dental aesthetics. The relation between the teeth and the smile line is the point of departure for aesthetic reconstruction of the front teeth. Lip position must be evaluated at rest, while speaking, with a moderately relaxed smile, and with a full smile. We must evaluate the exposure of the teeth and gums when the patient is completely relaxed and lips are positioned naturally. The mean smile line is described as showing 75-100% of the central incisors and interproximal papillae. A high smile line exposes more gum. A low smile line exposes less than 75% of the central incisor.1 The mean incisor exposure with the lips at rest is 1.91 mm in men and 3.40 mm in women. Exposure of more than 3 mm of gum is considered to be a «gummy» smile (Fig. 1). Cases of reconstruction of the front teeth in patients with a high smile line must be considered high risk.

Periodontal biotype and tooth morphology

The periodontal biotype is one of the most important factors in evaluating the prognosis of aesthetic restoration of the front teeth with implants. Depending on the biotype, the treatment plan has to be personalized to achieve an acceptable and lasting aesthetic result. Knowledge and analysis of the periodontal biotype allows us to establish realistic expectations for the outcome of the treatment plan.

Two periodontal biotypes that are related intimately to tooth morphology have been described² (Figs. 2 and 3):

1. Thin scalloped periodontal biotype: In this biotype the periodontal architecture is delicate and friable, with scant soft tissue. The thin periodontal biotype is associated to a specific dental morphology with anatomically triangular crowns, small interdental contact surfaces in the incisal third, and long thin papillae. The thin periodontal biotype responds to surgical and prosthodontic interventions with gum recession, apical migration of the periodontal anchorage, and loss of underlying alveolar volume, which results in an empty space known as a «black triangle». The thin periodontal biotype usually is accompanied by thin vestibular cortical bone with a tendency to form bone defects secondary to bone remodeling and resorption after tooth extraction or milling for implant placement.

The implantology team (surgeon, prosthodontist, and laboratory technician) have to coordinate their efforts to preserve the bone and soft tissue by using less aggressive surgical techniques and appropriate restoration procedures. In tooth extractions in patients with a thin periodontal biotype, it is recommended that alveolar crest preservation techniques be used, such as orthodontic tooth eruption, alveolar preservation, and guided bone regeneration,³ as well as soft tissue reinforcement, such as connective tissue grafts.⁴

2. Thick flat periodontal biotype: In this periodontal biotype, the soft tissue is dense and fibrotic, with abundant inserted tissue. The underlying bone is thick and dense. The dental crowns are square and convex in the cervical third. The contact points between crowns are long and often extend to the zone of the cervical third. Interdental papillae are short compared to the thin periodontal biotype. In this case, the response to surgical aggression is not gum recession but scar formation that can jeopardize the aesthetic and functional outcome.

 

Distance between implants and teeth

Knowledge of the implant-toimplant and implant-to-tooth distances is fundamental for achieving good aesthetic results. Correct three-dimensional placement (mesio-distal, vestibulo-palatal, and apico-coronal) of the implant in the bone will make an acceptable stable outcome possible (Table 1). The mesio-distal distance between an implant and a neighboring tooth should be at least 1.5 mm to maintain papilla integrity and achieve optimal aesthetic results. There should be at least 3 mm between adjacent implants^5,6 (Figs. 4 and 5). When two implants replace the two central incisors, the distance between implants should be at least 4 mm.³ At least 2 mm of vestibular table must be preserved on the vestibulo-palatal side so that the external surface of the implant is situated 2 mm palatally from an imaginary line delimited by the arc formed by the vestibular surface of the neighboring teeth (Fig. 6a) and the center of the implant is 2 mm palatally to this imaginary line. This is equivalent to the implant axis emerging from the basal ridge of the restored tooth. Finally, the implant should be 3 mm above the amelo-cementum junction in apicocoronal direction.^3,7-9 This is what Buser described as the comfort zone in the three spatial dimensions for correct implant placement in aesthetic restoration of the front teeth¹⁰ (Fig. 6b).

Reconstructive bone techniques

Guided bone regeneration (GBR)

Guided bone regeneration is a set of techniques that favor bone formation by protecting a bone defect against the invasion of nonosteogenic tissue. GBR is implemented using membranes with a certain permeability and tissue compatibility, which act as barriers to protect the defect against the invasion of fibroconnective tissue originating in the gingival mucosa.

The membrane must be biocompatible and impermeable; it must maintain the space so that stable regeneration can take place and It must be manageable and integrate with the surrounding connective tissue.

Membranes can be either absorbable or nonabsorbable. The most widely used nonabsorbable membranes are Gore-Tex (expanded poly (tetrafluoroethylene), e-PTFE). Use of these membranes has been well described by Simion¹¹ (Table 2). Membranes should be attached using microscrews or tacks, separated from the adjacent teeth and leaving space below the teeth for regeneration. These membranes have the drawback that they must be removed because they are not absorbable. They are very sensitive to the surgical technique and must be covered by a full-thickness flap. They can be reinforced with titanium to better resist soft-tissue pressure (Fig. 7) (Table 2). One of the most frequent complications¹² of these membranes is exposure and infection, which makes it necessary to remove the membrane. Simion reports a lower rate of bone regeneration when bone exposure and contamination occur than in unexposed membranes (41.6 versus 96.6%) and has confirmed in long-term studies that the bone obtained with GBR techniques and this type of membranes responds to implant placement much as mature native bone does.¹³

The absorbable membranes usually are collagen of bovine or porcine origin. They have the advantage of being more biocompatible with a lower rate of exposure.¹⁴ They do not have to be attached with screws or removed. In contrast with e-PTFE membranes, it is harder to maintain the resistance of absorbable membranes to soft tissues. Absorbable membranes can be used to cover both cortical and particulate bone grafts.¹⁵ In these cases it is helpful if graft absorption is minimized.^16,17 Nonabsorbable membranes also can be used in Schneider membrane perforations of the maxillary sinus.¹⁸

The barrier effect is more difficult to achieve with absorbable membranes so it is recommended that graft material be placed under these membranes.¹⁹

The literature does not generally show statistically significant differences between the use of absorbable and nonabsorbable membranes,^20,21 but a larger volume of bone regeneration is reported with nonabsorbable membranes in implants placed after tooth extraction.²² In the study reported by Chiapasco et al., there is a greater risk of exposure and contamination with nonabsorbable membranes that with bone grafts not covered with membrane.²³ Some evidence has been found that healing is better and there are fewer infections when the bone graft is covered by an absorbable membrane than by a nonabsorbable membrane.²⁴

Particulate grafts

Particulate grafts may be either autologous or biomaterials. They are used to fill self-retaining cavities. Better results have been reported in the literature when the graft is covered with a membrane.²⁵ The most important property of autologous bone is its osteogenicity. It also has osteoinductive and osteoconductive properties.

Particulate autologous bone grafts until recently were considered the «gold standard» in the scientific literature. They usually are obtained from intraoral zones using a bone scraper (from the bone adjacent to the bone defect, chin, or maxillomalar buttress) and can form mature bone in 9 months.²⁶ A larger volume of regenerated bone and more bone substitution are observed when the particle size is less than 2 mm³. ²⁷

Many biomaterials can be used as a particulate graft. Among the biomaterials available is hydroxyapatite, generally of bovine origin. The work of Hallman showed that when hydroxyapatite is mixed with autologous bone in a proportion of 80:20, its osteoconductive properties combine with the osteogenic and osteoinductive properties of autologous bone to produce more rapid and reliable bone regeneration with hardly any resorption.^28-30 The effect of the autologous bone is not clear, but it seems to reduce the usual healing time of 6 months.³¹ Our clinical experience has shown that the waiting time for implant placement could be reduced reliably to 4 months. Hydroxyapatite also can be mixed with autologous particulate bone time in 1:1 proportion.³²

Cortical grafts

Following the criteria published by Collins in 1995,³³ there are nine requirements for achieving success with block graft reconstruction:

1. The patient must have realistic and reasonable expectations about what is trying to be achieved.

2. Presurgical study of the case with preparation of models and wax casts of the desired prosthesis.

3. Preparation of a surgical splint.

4. Anatomic reconstruction of the defect.

5. Rigid graft fixation using at least two titanium osteosynthesis screws and making sure that the receptor bone and graft are in intimate contact.

6. Solid fixation of implants in the receptor bone.

7. The graft must be designed so that bone coverage of each face of the implant by at least 1.5 mm of bone is ensured after optimally positioning implants from a prosthodontic point of view. If this minimum thickness is not achieved, it is likely that graft resorption will expose the implant spiral. This point is especially relevant in grafts in the front tooth zone, where at least 2 mm of bone coverage on the vestibular face must be achieved.

8. Tension-free flap closure. Exposure to the intraoral medium is the most frequent cause of infection and graft loss.

9. Absence of pressure of the provisional prosthesis on the graft zone.

The cortical grafts most commonly used to restore the front tooth area are of intraoral origin: mandibular ramus and chin. Grafts from the mandibular ramus are associated with less morbidity than grafts from the chin area.^34,35 After clinical and radiologic examination and confirmation of the need for a cortical graft, a mucoperiosteal full thickness flap is made to expose the bone defect. The graft then is obtained, often using a piezoelectric scalpel to cut and adapt the cortical graft. The graft is attached with osteosynthesis screws and empty spaces are filled with a mixture of autologous bone obtained by scraping and hydroxyapatite or demineralized bone matrix. All the graft material is covered with an absorbable collagen membrane and sutured without tension using 5-0 and 6-0 monofilament.³⁶ Suture tension can be avoided by performing periosteotomy on the receptor bed of the graft prior to obtaining the graft, which ensures that bleeding secondary to graft harvesting occurs at the beginning of the intervention and not at the end. The cortical graft must be perfectly adapted and free of edges that can cause suture dehiscence or rubbing with the provisional prosthesis. The implant is placed in a second intervention at 4 months.^37–39

Mandibular ramus

This area is approached by means of an incision on the external oblique line, taking care not to injure the musculature of the buccal fat pad. It Is useful to carve the graft with a piezoelectric scalpel. The graft is raised with a chisel.

Mental symphysis

Cortical or cortico-cancellous graft is obtained from a zone limited laterally by the mental nerves and superiorly by the dental apices. A safety margin of 5 mm from these apices must be preserved. As in the mandibular ramus, a piezoelectric scalpel or fissure bur is useful.

Iliac crest

A large-volume cortical or cortico-cancellous bone graft of endochondral origin can be obtained from the hip. This bone is highly cellular and a saw and chisel are used for harvesting. Bone harvesting can cause discomfort in the donor area resulting in pain and limping. Injury to the femoral cutaneous nerve is one of the most frequent complications. The zone most often used is the anterosuperior iliac spine, which enables work on two fields and supplies sufficient bone. The posterosuperior iliac crest is used less but has been reported to produce less morbidity.⁴⁰

Skull

A cortical graft of membranous origin is obtained that results in little resorption. The donor zone does not cause discomfort and the scar is hidden by the hair. Complications are uncommon, so the graft is well tolerated by patients. However, the complications that occur can be very serious (cerebrospinal fluid fistulas, brain lesions). This donor area can be considered as an alternative to iliac crest grafts in large bone defects.⁴¹ The graft can be obtained with a bur and chisel. The external cortical generally is used, thus leaving the internal cortical intact. As the skull is of membranous origin, it experiences less resorption than the hip.⁴²

 

Clinical protocol

Small bone defect that does not compromise optimal implant placement

The patient’s periodontal biotype has to be assessed previously because a biomaterial does not jeopardize implant placement and will provide good cosmetic coverage of the defect in patients with a thick periodontal biotype. In patients with a thin periodontal biotype, a connective tissue graft is necessary (Scheme 1).

Parietal bone defect that compromises optimal implant placement

As in the previous section, a prophylactic connective tissue graft is recommended in the case of thin periodontal biotype. In these cases, the best reconstructive option is autologous bone graft obtained by scraping and mixed 1:1 with biomaterial (hydroxyapatite). The graft area is covered with an absorbable collagen membrane. A cortical graft or e-PTFE membrane also is a valid option, but autologous graft material collected by scraping is predictable, less aggressive than cortical grafts and safer than the e-PTFE membrane. In all three cases, mature bone without inflammatory tissue should be obtained by the fourth month (Scheme 2).

Two or three-wall bone defect

In patients with a thin periodontal biotype, a prophylactic connective tissue graft is recommended because a pediculated connective tissue graft can be made if the defect is large. In the case of two or three-wall bone defects, the best reconstructive option is cortical autologous graft because the grafts are not self-retaining. For defects less than 3 cm In diameter, the mandibular ramus followed by the chin are the sites of choices for bone harvesting. In our opinion, extraoral sites like the skull and iliac crest have to be used for defects larger than 3 cm. Empty spaces are filled with particulate autologous bone graft mixed 1:1 with biomaterial (hydroxyapatite). The cortical graft must be attached with two osteosynthesis screws. All the graft material should be protected by collagen membrane. Implants can be placed at 4 months (Scheme 3).

 

Clinical cases

The description of our protocol is illustrated by three clinical cases of implant placement for aesthetic reconstruction of front teeth. The cases have bone defects of different dimensions, each treated depending on the magnitude of the bone defect and characteristics of the patient’s periodontal biotype.

Clinical case 1

The patient had a chronic left lateral incisor lesion that required tooth extraction and GBR with nonabsorbable membrane. »A thin periodontal biotype and high smile line were risk factors (Figs. 8 a 19).

Clinical case 2

Patient referred for extraction of #23 with radicular fracture and possible fracture of #22, both with endodontia of long duration. Due to possible wall involvement, bone regeneration with a particulate graft was considered at the time of tooth extraction (Figs. 20 a 37).

Clinical case 3

A 24-year-old patient had suffered trauma that caused the loss of 21 when 16 years old. The patient consulted about replacing a removable acrylic prosthesis with an implantsupported prosthesis (Figs. 38 a 69).

 

 

Correspondence:
Jorge Caubet Biayna
GBCOM Clínica Juaneda
C/ Company, 30
07014 Palma de Mallorca. España
E-mail: jcaubet@telefonica.net

Recibido: 08.10.08
Aceptado: 02.03.09

 

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